Posts Tagged ‘IPv6’

Busting Myths – IPv6 Link Local Next Hop into BGP

August 30, 2015 2 comments

In some publications it is mentioned that a link local next-hop can’t be used when redistributing routes into BGP because routers receiving the route will not know what to do with the next-hop. That is one of the reason why HSRPv2 got support for global IPv6 addresses. One such scenario is described in this link.

The topology used for this post is the following.


I have just setup enough of the topology to prove that it works with the next-hop, so I won’t be running any pings and so on. The routers R1 and R2 have a static route for the network behind R3 and R4.

ipv6 route 2001:DB8:100::/48 GigabitEthernet0/1 FE80::5:73FF:FEA0:1

When routing towards a link local address, the exit interface must be specified. R1 then runs BGP towards R5, notice that I’m not using next-hop-self.

router bgp 100
bgp router-id
bgp log-neighbor-changes
neighbor 2001:DB8:1::5 remote-as 100
address-family ipv6
redistribute static
neighbor 2001:DB8:1::5 activate

If we look in the BGP RIB, we can see that the route is installed with a link local next-hop.

R1#sh bgp ipv6 uni
BGP table version is 2, local router ID is
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>  2001:DB8:100::/48
                                                0         32768 ?

What next-hop do we have at R5 though?

R5#sh bgp ipv6 uni
BGP table version is 10, local router ID is
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>i 2001:DB8:100::/48
                       2001:DB8:1::1            0    100      0 ?

We see the next-hop of R1 and not the link local address. How did this happen? We aren’t using next-hop-self. If we debug at R1, we will see what happens.

R1#debug ip bgp updates
R1#debug ip bgp ipv6 uni
*Aug 30 06:19:15.863: BGP(1): 2001:DB8:1::5 NEXT_HOP part 1 net 2001:DB8:100::/48, 
next FE80::5:73FF:FEA0:1
*Aug 30 06:19:15.863: BGP(1): Can't advertise 2001:DB8:100::/48 to 2001:DB8:1::5 
with NEXT_HOP FE80::5:73FF:FEA0:1
*Aug 30 06:19:15.863: BGP(1): (base) 2001:DB8:1::5 send UPDATE (format) 
2001:DB8:100::/48, next 2001:DB8:1::1, metric 0, path Local

We can see that BGP was going to advertise it with the link local next-hop but then realized that this would not work. It then replaced the link local next-hop with a global next-hop.

While it may have been true at some point that routes must point to a global next-hop, this does not hold true in modern code. BGP will automatically advertise its updates with a global next-hop.

Categories: BGP, IPv6 Tags: , , ,

IPv6 Multicast

July 14, 2015 2 comments

These are my notes for IPv6 multicast for the CCDE exam. Overview

  • Prefix FF::/8 reserved for multicast
  • Multicast Listener Discovery (MLD) replaces IGMP
    • MLD is part of ICMPv6
    • MLDv1 equivalent to IGMPv2
    • MLDv2 equivalent to IGMPv3
  • ASM, SSM and Bidir supported
  • PIM identified by IPv6 next header 103
  • BSR and static RP supported
  • No support for MSDP
    • Anycast supported through PIM, defined in RFC4610
  • Any Source Multicast (ASM)
    • PIM-SM, PIM-BiDir
    • Default for generic multicast and unicast prefix-based multicast
    • Starts with FF3x::/12
  • Source Specific Multicast (SSM)
    • PIM-SSM
    • FF3X::/32 is allocated for SSM by IANA
    • Currently prefix and plen is zero so FF3X::/96 is useable for SSM
  • Embedded RP groups
    • PIM-SM, PIM-BIDir
    • Starts with FF70::/12

IPv6 Multicast Addressing

IPv6 multicast address format includes variable bits to define what type of address it is and what the scope is of the multicast group. The scope can be:

1 – Node

2 – Link

3 – Subnet

4 – Admin

5 – Site

8 – Organization

E – Global

The flags define if embedded RP is used, if the address is based on unicast and if the address is IANA assigned or not (temporary). The unicast based IPv6 multicast address allows an organization to create globally unique IPv6 multicast groups based on their unicast prefixes. This is similar to GLOP addressing in IPv4 but does not require an Autonomous System Number (ASN). IPv6 also allows for embedding the RP address into the multicast address itself. This provides a static RP to multicast group mapping mechanism and can be used to provide interdomain IPv6 multicast as there is no MSDP in IPv6. When using Ethernet, the destination MAC address of the frame will start with 33:33 and the remaining 32 bits will consist of the low order 32 bits of the IPv6 multicast address.

Well Known Multicast Addresses

FF02::1 – All Nodes

FF02::2 – All Routers

FF02::5 – OSPF All Routers

FF02::6 – OSPF DR Routers

FF02::A – EIGRP Routers

FF02::D – PIM Routers

Neighbor Solicitation and DAD

IPv6 also uses multicast to replace ARP through the neighbor solicitation process. To do this the solicited node multicast address is used and the prefix is FF02::1:FF/104 and the last 24 bits are taken from the lower 24 bits of the IPv6 unicast address. If Host A needs to get the MAC of Host B, Host A will send the NS to the solicited node multicast address of B. IPv6 also does Duplicate Address Detection (DAD) to check that noone else is using the same IPv6 address and this also uses the solicited node multicast address. If Host A is checking uniqueness of its IPv6 address, the message will be sent to the solicited node multicast address of Host A.

Multicast Listener Discovery (MLD)

  • MLDv1 messages
    • Listener Query
    • Listener Report
    • Listener Done
  • MLDv2 messages
    • Listener Query
    • Listener Report

MLDv2 does not use a specific Done message which is equivalent to the Leave message in IGMP. It will stop sending Reports or send a Report which excludes the source it was previously interested in.

Protocol Independent Multicast (PIM) for IPv6

  • PIM-SM (RP is required)
    • Many to many applications (multiple sources, single group)
    • Uses shared tree initially but may switch to source tree
  • PIM-BiDir (RP is required)
    • Bidirectional many to many applications (hosts can be sources and receivers)
    • Only uses shared tree, less state
    • One to many applications (single source, single group)
    • Always uses source tree
    • Source must be learnt through out of band mechanism

Anycast RP

IPv6 does not have support for MSDP. It can support anycast RP through the use of PIM which can implement this feature. All the RPs doing anycast will use the same IPv6 address but they also require a unique IPv6 address that will be used to relay the PIM Register messages coming from the multicast sources. A RP-set is defined with the RPs that should be included in the Anycast RP and the PIM Register messages will be relayed to all the RPs defined in the RP-set. If the PIM Register message comes from an IPv6 address that is defined in the RP-set, the Register will not be sent along which is a form of split horizon to prevent looping of control plane messages. When a RP relays a PIM Register, this is done from a unique IPv6 address which is similar to how MSDP works.

Sources will find the RP based on the unicast metric as is normally done when implementing anycast RP. If a RP goes offline, messages will be routed to the next RP which now has the best metric.

Interdomain Multicast

These are my thoughts on interdomain multicast since there is no MSDP for IPv6. Embedded RP can be used which means that other organization needs to use your RP. Define a RP prefix that is used for interdomain multicast only or use a prefix that is used for internal usage but implement a data plane filter to filter out requests for groups that should not cross organizational boundaries. This could also be done by filtering on the the scope of the multicast address.

Another option would be to anycast RP with the other organization but this could get a lot messier unless a RP is defined for only a set of groups that are used for interdomain multicast. Each side would then have a RP defined for the groups and PIM Register messages would be relayed. The drawback would be that both sides could have sources but the policy may be that only one side should have sources and the other side only has listeners. This would be difficult to implement in a data plane filter. It might be possible to solve in the control plane by defining which sources the RP will allow to Register.

If using SSM, there is no need for a RP which makes it easier to implement interdomain multicast. There is always the consideration of joining two PIM domains but this could be solved by using static joins at the edge and implementing data plane filtering. Interdomain multicast is not something that is implemented a lot and it requires some thought to not merge into one failure domain and one administrative domain.

Final Thoughts

Multicast is used a lot in IPv6, multicast is more tightly integrated into the protocol than in IPv4, and it’s there even if you see it or not. The addressing, flags and scope can be a bit confusing at first but it allows for using multicast in a better way in IPv6 than in IPv4.

Categories: CCDE, IPv6 Tags: , , , ,

Service Provider IPv6 Deployment

June 29, 2015 2 comments

These are my study notes regarding IPv6 deployment in SP networks in preparation for the CCDE exam.

Drivers for implementing IPv6

  • External drivers
    • SP customers that need access to IPv6 resources
    • SP customers that need to interconnect their IPv6 sites
    • SP customers that need to interface with their own customers over iPv6
  • Internal drivers
    • Handle problems that may be hard to fix with IPv4 such as large number of devices (cell phones, IP cameras, sensors etc)
    • Public IPv4 address exhaustion
    • Private IPv4 address exhaustion
  • Strategic drivers
    • Long term expansion plans and service offerings
    • Preparing for new services and gaining competitive advantage


  • SP Core Infrastructure
    • Native IPv4 core
    • L2TPv3 for VPNs
    • MPLS core
    • MPLS VPNs

My reflection is that most cores would be MPLS enabled, however there are projects such as Terastream in Deutsche Telekom where the entire core is IPv6 enabled and L2TPv3 is used in place of MPLS.

  • IPv6 in Native IPv4 Environments
    • Tunnel v6 in v4
    • Native v6 with dedicated resources
    • Dual stack

The easiest way to get going with v6 was to tunnel it over v4. The next logical step was to enable v6 but on separate interfaces to not disturb the “real” traffic and to be able to experiment with the protocol. The end goal is dual stack, at least in a non MPLS enabled network.

  • IPv6 in MPLS environments
    • 6PE
    • 6VPE

6PE is a technology to run IPv6 over an IPv4 enabled MPLS network. 6VPE does the same but with VRFs.

  • Native IPv6 over Dedicated Data Link
    • Dedicated data links between core routers
    • Dedicated data links to IPv6 customers
    • Connection to an IPv6 IX
  • Dual stack
    • All P + PE routers capable of v4 + v6 transport
    • Either two IGPs or one IGP for both v4 + v6
    • Requires more memory due to two routing tables
    • IPv6 multicast natively supported
    • All IPv6 traffic is routed in global space (no MPLS)
    • Good for content distribution and global services (Internet)
  • 6PE
    • IPv6 global connectivity over an IPv4 MPLS core
    • Transition mechanism (debatable)
    • PEs are dual stacked and need 6PE configuration
    • IPv6 reachability exchanged via MPBGP over iBGP sessions
    • IPv6 packets transported from 6PE to 6PE inside MPLS
    • The next-hop is an IPv4 mapped IPv6 address such as ::FFFF:
    • BGP label assigned for the IPv6 prefix
    • Bottom label used due to P routers not v6 capable and for load sharing
    • neighbor send-label is configured under BGP address-family ipv6

6PE is viewed as a transition mechanism but this is arguable, if you transport IPv4 over MPLS, you may want to do the same with IPv6 as well for consistency. Running 6PE means that there is fate sharing between v4 and v6 though, which could mean that an outage may affect both protocols. This could be avoided by running MPLS for IPv4 but v6 natively.

  • Core network (P routers) left untouched
  • IPv6 traffic inherits MPLS benefits such as fast-reroute and TE
  • Incremental deployment possible (upgrade PE routers first)
  • Each site can be v4-only, v4-VPN-only, v4+v6, v4-VPN+v6 and so on
  • Scalability concerns due to separate RIB and FIB required per customer
  • Mostly suitable for SPs with limited amount of PEs
  • 6vPE
    • Equivalent of VPNv4 but for IPv6
    • Add VPNv6 address family under MPBGP
    • Send extended communities for the prefixes under the address family

It is a common misconception for 6PE and 6vPE that traceroutes are not possible, that is however not entirely true. A P router can generate ICMPv6 messages that will follow the LSP to the egress PE and then the ICMPv6 error message is forwarded back to the originator of the traceroute.

  • Route reflectors for 6PE and 6vPE
    • Needed to scale BGP full mesh
    • Dedicated RRs or data path RRs
    • Either dedicated RR per AF or have multiple AFs per RR
    • 6PE-RR must support IPv6 + label functionality
    • 6vPE-RR must support IPv6 + label and extended communities functionality

PA vs PI

  • PA advantages
    • Aggregation towards upstreams
    • Minimizes Internet routing table size
  • PA disadvantages
    • Customer is “locked” with the SP
    • Renumbering can be painful
    • Multi-homing and TE problems

The main driver here is if you are going to multi home or not. Renumbering is always painful but at least less so on IPv6 due to being able to advertise multiple IPv6 prefixes through Router Advertisements (RA).

  • PI advantages
    • Customers are not “locked” to the SP
    • Multi homing is straight forward
  • PI disadvantages
    • Larger Internet routing table due to lack of efficient aggregation
    • Memory and CPU needs on BGP speakers

Infrastructure Addressing (LLA vs global)

What type of addresses should be deployed on infrastructure links?

  • Link Local Address FE80::/10
    • Non routeable address
    • Less attack surface
    • Smaller routing tables
    • Can converge faster due to smaller RIB/FIB
    • Less need for iACL at edge of network
    • Can’t ping links
    • Can’t traceroute links
    • May be more complex to manage with NMS
    • Use global address on loopback for ICMPv6 messages
    • Will not work with RSVP-TE tunnels
  • Global only 2000::/3 (current IANA prefix)
    • Globally routeable
    • Larger attack surface unless prefix suppression is used
    • Use uRPF and iACL at edge to protect your links
    • Easier to manage

It would be interesting to hear if you have seen any deployments with LLA only on infrastructure links. In theory it’s a nice idea but it may corner you in some cases, preventing you from implementing other features that you wish to deploy in your network.

Use /126 or /127 on P2P links which is the equivalent of /30 or /31 on IPv4 links. For loopbacks use /128 prefixes. Always assign addresses from a range so that creating ACLs and iACLs becomes less tedious.

Using another prefix than /64 on an interface will break the following features:

  • Neighbor Discovery (ND)
  • Secure Neighbor Discovery (SEND)
  • Privacy extensions
  • PIM-SM with embedded RP

This is of course for segments where there are end users.

Prefix Allocation Practices

  • Many SPs offer /48, /52, /56, /60 or /64 prefixes
  • Enterprise customers receive one /48 or more
  • Small business customers receive /52 or /56 prefix
  • Broadband customers may receive /56 or /60 via DHCP Prefix Delegation (DHCP-PD)

Debating prefix allocation prefixes is like debating religion, politics or your favourite OS. Whatever you choose, make sure that you can revise your practice as future services and needs arrise.

Carrier Grade NAT(CGN)

  • Short term solution to IPv4 exhaustage without changing Residential Gateway (RG) or SP infrastructure
  • Subscriber uses NAT44 and SP does CGN with NAT44
  • Multiplexes several customers onto the same public IPv4 address
  • CGN performance and capabilities should be analysed in the planning phase
  • May provide challenges in logging sessions
  • Long term solution is to deploy IPv6

I really don’t like CGN, it slows down the deployment of IPv6. It’s a tool like anything else though that may be used selectively if there is no other solution available.

IPv6 over L2TP Softwires

  • Dual stack IPv4/IPv6 on RG LAN side
  • PPPoE or IPv4oE terminated on v4-only BNG
  • L2TPv2 softwire between RG and IPv6-dedicated L2TP Network Server (LNS)
  • Stateful architecture on LNS
    • Offers dynamic control and granular accounting of IPv6 traffic
  • Limited investment needed and limited impact on existing infrastructure

I have never seen IPv6 deployed over softwires, what about you readers?


  • Uses 6RD CE (Customer Edge) and 6RD BR (Border Relay)
  • Automatic prefix delegation on 6RD CE
  • Stateless and automatic IPv6 in IPv4 encap and decap functions on 6RD
  • Follows IPv4 routing
  • 6RD BRs are adressed with IPv4 anycast for load sharing and resiliency
  • Limited investment and impact on existing infrastructure

IPv4 via IPv6 Using DS-Lite with NAT44

  • Network has migrated to IPv6 but needs to provide IPv4 services
  • IPv4 packets are tunneled over IPv6
  • Introduces two components: B4 (Basic Bridging Broadband Element) and AFTR (Address Family Transition Router)
    • B4 typically sits in the RG
    • AFTR is located in the core infrastructure
  • Does not provide IPv4 and IPv6 hosts to talk to each other
  • AFTR device terminates the tunnel and decapsulates IPv4 packet
  • AFTR device performs NAT44 on customer private IP to public IP addresses
  • Increased MTU, be aware of fragmentation

Connecting IPv6-only with IPv4-only (AFT64)

  • Only applicable where IPv6-only hosts need to communicate with IPv4-only hosts
  • Stateful or stateless v6 to v4 translation
  • Includes NAT64 and DNS64

MAP (Mapping of Address and Port)

  • MAP-T Stateless 464 translation
  • MAP-E Stateless 464 encapsulation
  • Allows sharing of IPv4 address across an IPv6 network
    • Each shared IPv4 endpoint gets a unique TCP/UDP port range via “rules”
    • All or part of the IPv4 address can be derived from the IPv6 prefix
      • This allows for route summarization
    • Need to allocate TCP/UDP port ranges to each CPE
  • Stateless border relays in SP network
    • Can be implemented in hardware for superior performance
    • Can use anycast and have asymmetric routing
    • No single point of failure
  • Leverages IPv6 in the network
  • No CGN inside SP network
  • No need for logging or ALGs
  • Dependent on CPE router


  • Stateful or stateless translation
  • Stateful
    • 1:N translation
    • “PAT”
    • TCP, UDP, ICMP
    • Shares IPv4 addresses
  • Stateless
    • 1:1 translation
    • “NAT”
    • Any protocol
    • No IPv4 address savings

DNS64 is often required in combination with NAT64 to send AAAA response to the IPv6-only hosts in case the server only exists in the v4 world.


  • Somewhere around 15% of apps break with native v6 or NAT64
  • Skype is one of these apps
  • 464XLAT can help with most of these applications
  • Handset does stateless 4 to 6 translation
  • Network does NAT64
  • Deployed by T-Mobile
Categories: CCDE, IPv6 Tags: , ,

A Quick Look at NAT64 and NAT46

August 26, 2014 3 comments


In the best of worlds we would all be using native IPv6 now, or at least dual
stack. That is not the case however and IPv4 will be around for a long time yet.
During that time that both protocols exist, there will be a need to translate
between the two, like it or not.

Different Types of NAT

Before we begin, let’s define some different forms of NAT:

NAT44 – NAT from IPv4 to IPv4
NAT66 – NAT from IPv6 to IPv6
NAT46 – NAT from IPv4 to IPv6
NAT64 – NAT from IPv6 to IPv4

The most commonly used type is definitely NAT44 but here we will focus on translating
between IPv4 and IPv6.


There are two different forms of NAT64, stateless and statefull. The stateless version
maps the IPv4 address into an IPv6 prefix. As the name implies, it keeps no state.
It does not save any IP addresses since every v4 address maps to one v6 address.
Here is a comparison of stateless and statefull NAT64:



When resolving names to numbers in IPv4, A records are used. When doing the same
in IPv6, AAAA records are used. When using NAT64, the device doing the translation
will translate between A and AAAA records. The function of DNS64 will not be
described further in this post.


The configuration guides at are pretty poorly written and there is
not much else to find on configuring NAT64 on ASA. That’s always one of my goals
with a blog post, to learn a topic and to help spread knowledge into the networking

The Lab

To demonstrate NAT64, the following topology is used:


The goal is for IOS9 to source traffic from its loopback 2001:db8:0:9::9 to
IOS7 with the IP address The routers have some basic configuration
with IP addresses on the interfaces and static routing.


interface GigabitEthernet0/0
 ip address
ip route


ipv6 unicast-routing
interface GigabitEthernet0/0
 ipv6 address 2001:DB8::2/64
interface GigabitEthernet0/1
 ipv6 address 2001:DB8:0:1::2/64
ipv6 route 2001:DB8:0:9::9/128 2001:DB8:0:1::1
ipv6 route ::/0 2001:DB8::1


ipv6 unicast-routing
interface Loopback0
 ipv6 address 2001:DB8:0:9::9/64
interface GigabitEthernet0/0
 ipv6 address 2001:DB8:0:1::1/64
ipv6 route ::/0 2001:DB8:0:1::2

The ASA is the device that will be doing the NAT64. It has one IPv4 interface and
one IPv6 interface. It starts with the following configuration:


interface GigabitEthernet0/0
 nameif inside
 security-level 100
 ip address 
interface GigabitEthernet0/1
 nameif outside
 security-level 0
 no ip address
 ipv6 address 2001:db8::1/64
access-list outside extended permit icmp6 any any 
ipv6 route outside 2001:db8:0:9::9/128 2001:db8::2

In newer versions of ASA code, unified ACL is supported. That means we can have
both IPv4 and IPv6 in the same ACL. In my ACL I am allowing ICMPv6 to come in
on the “outside” interface.

To translate between IPv6 and IPv4, NAT must be configured. Both object NAT and
twice NAT is supported but I prefer twice NAT, so that is what I will configure.

When pinging from IOS9, we need to define an address that will represent IOS7 (IPv6).
This is the destination of the packet. The source address of IOS9 needs to be translated
to an IPv4 address as well. This picture will show the flow of the traffic:


Time to configure the ASA. The traffic flow is coming in on the interface “outside”
and exiting on interface “inside”. We need to define network objects, try to name
them properly because otherwise it can be confusing to understand the traffic flow.

object network REALv6_OUTSIDE
host 2001:db8:0:9::9
object network MAPPED_IPv4_INSIDE
object network MAPPED_IPv6_OUTSIDE
host 2001:db8:0:a::2
object network REALv4_INSIDE
nat (outside,inside) source static REALv6_OUTSIDE MAPPED_IPv4_INSIDE destination 
static MAPPED_IPv6_OUTSIDE REALv4_INSIDE net-to-net

The syntax can be a bit confusing so let’s take a closer look:

REALv6_OUTSIDE – This is the source IP(v6) of IOS9
MAPPED_IPv4_INSIDE – This is what IOS9 gets translated to on the inside
MAPPED_IPv6_OUTSIDE – This is the destination IOS9 is sending traffic to
REALv4_INSIDE – This is what the destination gets translated to on the inside

To test our setup, we will ping from IOS9:

IOS9#ping 2001:DB8:0:A::2 so lo0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:DB8:0:A::2, timeout is 2 seconds:
Packet sent with a source address of 2001:DB8:0:9::9
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/5/11 ms
IOS7#debug ip icmp
ICMP packet debugging is on
*Aug 26 07:28:27.786: ICMP: echo reply sent, src, dst, topology BASE, dscp 0 topoid 0
*Aug 26 07:28:27.796: ICMP: echo reply sent, src, dst, topology BASE, dscp 0 topoid 0
*Aug 26 07:28:27.802: ICMP: echo reply sent, src, dst, topology BASE, dscp 0 topoid 0
*Aug 26 07:28:27.810: ICMP: echo reply sent, src, dst, topology BASE, dscp 0 topoid 0
*Aug 26 07:28:27.811: ICMP: echo reply sent, src, dst, topology BASE, dscp 0 topoid 0

That worked! Let’s take a look at the XLATE table:

ASA1#  show xlate
2 in use, 2 most used
Flags: D - DNS, e - extended, I - identity, i - dynamic, r - portmap,
       s - static, T - twice, N - net-to-net
NAT from outside:2001:db8:0:9::9/128 to inside:
    flags sTN idle 0:01:04 timeout 0:00:00
NAT from inside: to outside:2001:db8:0:a::2/128
    flags sTN idle 0:01:04 timeout 0:00:00

That was ICMP. How about TCP? We need to allow TCP through the firewall.

ASA1(config)# access-list outside permit tcp any any
IOS7(config)#username nat password nat
IOS7(config)#line vty 0 4
IOS7(config-line)#login local
IOS9#telnet 2001:DB8:0:A::2 /source-interface lo0
Trying 2001:DB8:0:A::2 ... Open

User Access Verification


No matter what you think of NAT, that is pretty cool!

ASA1# show conn
1 in use, 4 most used

TCP outside inside, idle 0:00:43, bytes 2805, flags UIOB

ASA1# show nat det
Manual NAT Policies (Section 1)
1 (outside) to (inside) source static REALv6_OUTSIDE MAPPED_IPv4_INSIDE   destination static MAPPED_IPv6_OUTSIDE REALv4_INSIDE net-to-net
    translate_hits = 6, untranslate_hits = 24
    Source - Origin: 2001:db8:0:9::9/128, Translated:
    Destination - Origin: 2001:db8:0:a::2/128, Translated:

This was NAT64 in action. With our NAT we were doing one to one translation
between IPv6 and IPv4. If IPv4 addresses are scarce, we can define a NAT
pool and translate to that.

ASA1(config)# object network IPv4_POOL
ASA1(config-network-object)# range
ASA1(config-network-object)# exit
ASA1(config)# nat (outside,inside) source dynamic REALv6_OUTSIDE pat-pool IPv4_POOL
destination static MAPPED_IPv6_OUTSIDE REALv4_INSIDE net-to-net
IOS9#telnet 2001:db8:0:a::2 /source-interface lo0
Trying 2001:DB8:0:A::2 ... Open

User Access Verification


ASA1# show xlate
2 in use, 3 most used
Flags: D - DNS, e - extended, I - identity, i - dynamic, r - portmap,
       s - static, T - twice, N - net-to-net
NAT from inside: to outside:2001:db8:0:a::2/128
    flags sTN idle 0:00:42 timeout 0:00:00

TCP PAT from outside:2001:db8:0:9::9/43376 to inside: flags ri idle 0:00:42 timeout 0:00:30
ASA1# show nat detail
Manual NAT Policies (Section 1)
1 (outside) to (inside) source dynamic REALv6_OUTSIDE pat-pool IPv4_POOL  destination static MAPPED_IPv6_OUTSIDE REALv4_INSIDE net-to-net
    translate_hits = 9, untranslate_hits = 10
    Source - Origin: 2001:db8:0:9::9/128, Translated (PAT):
    Destination - Origin: 2001:db8:0:a::2/128, Translated:

ASA1# show conn
1 in use, 4 most used

TCP outside inside, idle 0:00:01, bytes 1382, flags UIOB 

The source got translated to through PAT.


IPv6 is here to stay, but so is also IPv4 for a long time to come. Personal
opinions aside, we may need to translate between IPv6 and IPv4 for a time to
come. Knowing how to configure NAT64 is just another tool in our belt.

Categories: IPv6, NAT Tags: , , ,

Cisco updates the Catalyst 2960 – Catalyst 2960-X and Catalyst 2960-XR

June 12, 2013 1 comment

The Catalyst 2960 is a very common switch in any environment that has
Cisco devices. A couple of years ago the 2960 got stacking via the
2960-S model. It also got the ability to do static routes which
was a nice feature. I used it in some deployments to do routing
locally in 2960 and then add a default route towards WAN provider.
That way I didn’t have to go through a slow CPE to route my local

The 2960-X and -XR are available in 24 or 48 port configurations.
Uplinks are either 2x 10 Gbit SPF+ or 4x 1 Gbit SFP. The PoE models
can support 370W or 740W of power.

The 2960-X provides up to 80 Gbps of stack bandwidth which is 2x more
compared to the 2960-S. It is now also possible to stack up to 8 switches
compared to the earlier maximum of 4. The 2960-S model uses FlexStack while
the newer -X and -XR models uses FlexStack-Plus. FlexStack-Plus supports
detecting stack port operational state in hardware and change the forwarding
according to it. This takes 100 ms or less. The older model does it in CPU
which can take 1 or 2 seconds.

Here are some notable differences between 2960-X and -XR compared to 2960-S.

  • Dual core CPU @ 600 MHz. 2960-S has single core
  • 2960-XR has support for dual power supplies
  • 256 MB of flash for -XR, 128 MB for -X. The S model has 64 MB
  • 512 MB of DRAM compared to 256 for 2960-S
  • 1k active VLANs compared to 255 for 2960-S
  • 48 Etherchannel groups for -XR, 24 for -X and 6 for -S
  • 4 MB of egress buffers instead of 2 MB
  • 4 SPAN sessions instead of 2
  • 32k MACs for -XR, 16k for -X and 8k for -S
  • 24k unicast routes for -XR, 16 static routes for -X and -S

The newer models also support Netflow lite, hibernation mode and EEE.

The 2960-XR does support dynamic routing. It has support for RIP, OSPF stub,
OSPFv3 stub, EIGRP stub, HSRP, VRRP and PIM.

Here are some performance numbers:

2960-X Lan Lite has 100 Gbps of switching bandwidth and 64 active VLANS.
2960-X Lan Base has 216 Gbps of switching bandwidth and 1023 active VLANs.
The same holds true for 2960-XR with IP Lite feature set. The 2960-S had
a maximum of 255 VLANs and 176 Gbps switching bandwidth. Depending on
model the 2960-X tops out at 130.9 Mpps compared to 101.2 for 2960-S.

The switches also have added support for IPv6. Notable features are:

  • IPv6 MLDv1 and v2 snooping
  • IPv6 First Hop Security (RA guard, source guard, and binding integrity guard
  • IPv6 ACLs
  • IPv6 QoS
  • HTTP/HTTPs over IPv6
  • SNMP over IPv6
  • Syslog over IPv6

I’m expecting more information to come out as it gets presented during Cisco Live
in Orlando.

IPv6 operation and best practices – documents to read

March 22, 2013 3 comments

Unfortunately I don’t get to do much v6 at my job yet but I still like to stay updated on
what is happening. Do you run any v6 in your network? If so, do you run it native or tunneled
or something like 6PE?

Here are some interesting sources for operation of v6.


This document discusses if IPv4 and IPv6 traffic
should be mixed on the same interface or should different interfaces be used? Should
link local or global addressing be used for routing? Should v6 routes be transferred
over v4 in BGP sessions?


This document is for deploying v6 in an enterprise network. Things like security policy,
addressing plan and IPv6 myths are brought up.


This document is purely about the advantages and disadvantages of only running link local

Also, don’t miss out on information that is freely available at Cisco Live. Here are
some interesting sessions on IPv6 from Melbourne.

BRKRST-2301 – Enterprise IPv6 Deployment (2013 Melbourne)
BRKRST-1069 – Understanding IPv6 (2013 Melbourne)
ITMGEN-1313 – Preparing for IPv6 in the Enterprise (2013 Melbourne)
BRKRST-2311 – IPv6 Planning, Deployment and Troubleshooting (2013 Melbourne)
BRKSEC-2003 – IPv6 Security Threats and Mitigations (2013 Melbourne)
COCRST-2464 – Inside Cisco IT: Making The Leap To IPv6 (2013 Melbourne)

As you can see. IPv6 is a pretty big deal these days at Cisco Live. Then you also have
books, configuration guides etc but this should give you a good start to see what challenges
and considerations you should have when deploying IPv6.

Categories: IPv6 Tags: , , ,

EIGRP named configuration

March 15, 2013 6 comments

You might think that EIGRP being around for so long is not getting any attention from
Cisco, not true. EIGRP is still being developed and in later releases you can run what
is called named configuration. Doing this you can put all EIGRP config under one named
instance, even v6 which is different from the old syntax. If you are on Twitter you should
follow Donnie Savage @diivious. He works for Cisco and is usually present at Cisco Live
presenting on the development of EIGRP.

We start out with the following topology.


So we start out by defining our instance and calling it corp

R2#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R2(config)#router eigrp corp

From there we have the following options:

Router configuration commands:
  address-family  Enter Address Family command mode
  default         Set a command to its defaults
  exit            Exit from routing protocol configuration mode
  no              Negate a command or set its defaults
  service-family  Enter Service Family command mode
  shutdown        Shutdown this instance of EIGRP

From here we can shutdown the process or configure different address families.
We start by setting up IPv4 in the global table.

R2(config-router)#address-family ipv4 autonomous-system 12
Address Family configuration commands:
  af-interface         Enter Address Family interface configuration
  default              Set a command to its defaults
  eigrp                EIGRP Address Family specific commands
  exit-address-family  Exit Address Family configuration mode
  help                 Description of the interactive help system
  maximum-prefix       Maximum number of prefixes acceptable in aggregate
  metric               Modify metrics and parameters for address advertisement
  neighbor             Specify an IPv4 neighbor router
  network              Enable routing on an IP network
  no                   Negate a command or set its defaults
  shutdown             Shutdown address family
  timers               Adjust peering based timers
  topology             Topology configuration mode

From here we define networks, setup static neighbors and configure EIGRP parameters.

We will use regular syntax on R2 for setting up EIGRP.

R2(config-if)#router eigrp 12
R2(config-router)#no auto

The session comes up.

%DUAL-5-NBRCHANGE: EIGRP-IPv4 12: Neighbor (FastEthernet1/0) is up: new adjacency

R2 is announcing it’s loopback. Lets see if we receive that.

R1#sh ip route eigrp | be Gateway
Gateway of last resort is not set is subnetted, 1 subnets
D [90/2662400] via, 00:00:23, FastEthernet1/0

What more can we configure under the address-family?

R1(config-router-af)#af-interface f1/0
Address Family Interfaces configuration commands:
  authentication      authentication subcommands
  bandwidth-percent   Set percentage of bandwidth percentage limit
  bfd                 Enable Bidirectional Forwarding Detection
  dampening-change    Percent interface metric must change to cause update
  dampening-interval  Time in seconds to check interface metrics
  default             Set a command to its defaults
  exit-af-interface   Exit from Address Family Interface configuration mode
  hello-interval      Configures hello interval
  hold-time           Configures hold time
  next-hop-self       Configures EIGRP next-hop-self
  no                  Negate a command or set its defaults
  passive-interface   Suppress address updates on an interface
  shutdown            Disable Address-Family on interface
  split-horizon       Perform split horizon
  summary-address     Perform address summarization

We configure all EIGRP interface commands under the af-interface. We can setup
authentication of the peering.

R1(config-router-af)#af-interface f1/0
R1(config-router-af-interface)#authentication mode ?
  hmac-sha-256  HMAC-SHA-256 Authentication
  md5           Keyed message digest
R1(config-router-af-interface)#authentication mode md5
R1(config-router-af-interface)#authentication key-chain EIGRP
%DUAL-5-NBRCHANGE: EIGRP-IPv4 12: Neighbor (FastEthernet1/0) is down: authentication mode changed
%DUAL-5-NBRCHANGE: EIGRP-IPv4 12: Neighbor (FastEthernet1/0) is up: new adjacency

What’s new here is that sha-256 is now also supported. From this af-interface mode
we can configure timers and BFD as well.

Now we will configure IPv4 in a VRF called 13.

R1(config)#vrf definition 13
R1(config-vrf)#rd 13:13
R1(config-vrf)#int f1/1
R1(config-if)#no sh
R1(config-if)#vrf forwarding 13
R1(config-if)#ip add
R1(config-router)#address-family ipv4 vrf 13 autonomous-system 13
%DUAL-5-NBRCHANGE: EIGRP-IPv4 13: Neighbor (FastEthernet1/1) is up: new adjacency

Do we receive any prefixes?

R1#sh ip route vrf 13 | be Gate
Gateway of last resort is not set is subnetted, 1 subnets
D [90/2662400] via, 00:00:31, FastEthernet1/1 is variably subnetted, 2 subnets, 2 masks
C is directly connected, FastEthernet1/1
L is directly connected, FastEthernet1/1

Which we do. Nothing strange here, just a new syntax for defining VRFs compared
to the old ip vrf syntax.

Finally we will configure IPv6 peering as well. Because EIGRP sends packets from
link local address we don’t even need to configure a global IPv6 address.

R1(config-router)#int f2/0
R1(config-if)#ipv6 enable
R1(config-if)#no sh
R1(config-if)#router eigrp corp
R1(config-router)#address-family ipv6 autonomous-system 14
R1(config-router-af)#af-interface default
R1(config-router-af-interface)#no shut

Only difference here is that instead of defining network we use the interface command
instead to enable it on all active IPv6 interfaces.

R1#sh ipv6 route eigrp
IPv6 Routing Table - default - 2 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
       B - BGP, R - RIP, H - NHRP, I1 - ISIS L1
       I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary, D - EIGRP
       EX - EIGRP external, ND - ND Default, NDp - ND Prefix, DCE - Destination
       NDr - Redirect, O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1
       OE2 - OSPF ext 2, ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2, l - LISP
D   2001::/64 [90/2662400]
     via FE80::C803:82FF:FE80:1C, FastEthernet2/0

And that’s about it. Named configuration is made to unify configuration under
one instance and remove the commands that we used to type under the interface
like authentication and such. It’s now all done under the address-family.
In future posts I will look at Multi Topology Routing (MTR).