Archive for October, 2010

Notes on RIP

October 25, 2010 Leave a comment

RIP is not as common these days as it used to be but it can still have its uses in small networks. It is also still tested in the CCIE lab. Here are some notes I have written down.

  • RIP is a distance vector protocol
  • Uses UDP port 520 as transport
  • Uses split-horizon (does not send updates back the same way it was received)
  • Broadcasts updates every 30 seconds
  • Uses hopcount as metric
  • Maximum hopcount is 15, 16 hops is inaccessible
  • Classful routing

RIP version 2 is defined in RFC 1723 by G.Malkin
Version 2 brings:

  • Subnetmask
  • Authentication
  • Multicast instead of broadcast
  • Route tag
  • Next-hop

The biggest improvement is sending the subnetmask in updates which means RIP is classless.
Plain text authentication is defined in the RFC but Cisco also supports MD5.
The packets are multicasted to instead of broadcast.
Routes can be tagged with the source they originated from or to tag as a filtering mechanism.
Next-hop carried in update in case route is to non RIP speaking router.

As all distance vector protocols RIP uses split-horizon, this can pose a problem when interfaces have secondary addresses or when multipoint interfaces are used. To advertise more than one network per interface split-horizon has to be disabled. This is done with no ip slit-horizon in interface configuration mode.

RIP uses auto-summarization by default. To turn it off use no auto-summary under the router rip process. Note that advertising
supernets larger than their classful boundary is not supported as seen below:

Router(config-if)#ip summary-address rip
Summary mask must be greater or equal to major net

The Cisco implementation of RIP has support for triggered updates, but only on serial point-to-point interfaces. It is enabled with ip rip triggered under the interface and it will supress periodic updates and only send updates when necessary.

To change between RIP versions you can either set the version globally with the version command under the router rip process or set it per interface with ip rip send and ip rip receive version commands. The interface specific command overrides the globally set version. If you want to send a RIP version 2 packet but broadcast it because multicast is not available this is also an option. Use ip rip v2-broadcast.

RIP version 2 has supportfor authentication either in plain text or with MD5, the MD5 extension is defined in RFC 2082. To set the mode use ip rip authentication mode text | md5. Then you need to configure a key-chain and configure RIP to use it with ip rip authentication key-chain name-of-keychain.

Categories: CCIE, Notes, Routing Tags: , , ,

Update – computer crashed and frame-relay

October 14, 2010 Leave a comment

A week ago I had to send my laptop to service because it was behaving very badly. Also been really busy at work, implementing a new customer. I have done some studying, frame-relay is the topic right now. Although I recognize that the CCIE is a technology test and from that perspective frame-relay is a good technology to test I don’t really see the use for it. I live in Sweden and there is no frame-relay here, we have Ethernet and Gigabit links or faster pretty much everywhere and frame-relay just isn’t used any more. On the other hand frame-relay has some simularities with MPLS and I guess it’s never a bad thing to learn a technology and to have a feel for the history of networking. Are any of you still getting exposure to frame-relay?

Categories: Announcement Tags:

September – disappointing amount of study

October 3, 2010 Leave a comment

I’m far from pleased with the study result for September. I was on vacation in the beginning on the month and then work has been crazy lately since we’ve replaced our entire LAN. This wednesday I worked 18 hours straight which might be a new record 😛 I’ve only done about 12 hours of reading for September which is hugely disappointing. This only motivates me to pick up the pace though. October will have to be much better than that. Hoping to hit the 100 mark when October is done. Going to do a recap of spanning tree and then move on to frame relay.

Categories: Announcement, CCIE Tags: ,