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How does RIP automatic summarization work? How do you turn off auto-summary of routes? Does it matter?
The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols which employ the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from source to destination. The largest number of hops allowed for RIP is 15, which limits the size of networks that RIP can support.
RIP implements the split horizon, route poisoning and holddown mechanisms to prevent incorrect routing information from being propagated.
In RIPv1 router broadcast updates with their routing table every 30 seconds. In the early deployments, routing tables were small enough that the traffic was not significant. As networks grew in size, however, it became evident there could be a massive traffic burst every 30 seconds, even if the routers had been initialized at random times.
In most networking environments, RIP is not the preferred choice for routing as its time to converge and scalability are poor compared to EIGRP, OSPF, or IS-IS. However, it is easy to configure, because RIP does not require any parameters unlike other protocols.
RIP uses the User Datagram Protocol (UDP) as its transport protocol, and is assigned the reserved port number 520
Based on the Bellman–Ford algorithm and the Ford–Fulkerson algorithm distant-vector routing protocols started to be implemented from 1969 onwards in data networks such as the ARPANET and CYCLADES. The predecessor of RIP was the Gateway Information Protocol (GWINFO) which was developed by Xerox in the mid-1970s to route its experimental network. As part of the Xerox Network Systems (XNS) protocol suite GWINFO transformed into the XNS Routing Information Protocol. This XNS RIP in turn became the basis for early routing protocols, such as Novell’s IPX RIP, AppleTalk’s Routing Table Maintenance Protocol (RTMP), and the IP RIP. The 1982 Berkley Software Distribution of the UNIX operating system implemented RIP in the routed daemon. The 4.2BSD release proved popular and became the basis for subsequent UNIX versions, which implemented RIP in the routed or gated daemon. Ultimately RIP had been extensively deployed before the standard written by Charles Hedrick was passed as RIPv1 in 1988.
Transcription:
Best practice is to disable automatic summarization.
So on router 3 at the moment, we don’t have automatic summarization disabled. It is disabled on Router 2 and router 1. We disabled automatic summarization here on Router 2 and here on router 1.
So on router 3
router rip no auto-summary
Now it may take RIP a while to converge. So do force things I’m simply going to turn off packet tracer and turn it on again. So I’ll close packet tracer here and I’ll start it up again. I found that with packet tracer sometimes when you make changes like ths, the best way to ensure that things are working properly, is to simply restart packet tracer.
Okay, so packet tracer has booted up again.
show ip route
this router has now learned about this network. Notice it’s a /24 network, not a /16.
So show ip rip database
we see this network rather than a /16 in the RIP database. Router 3 is not automatically summarizing this route.
So the network will function as it was before but is more reliable because we are not automatically summarizing routes. You need to be careful with automatic summarization. Best practice is to generally turn off automatic summarization in routing protocols such as RIP and EIGRP. You don’t want automatic summarization in a network because as an example, if you had a 172.16 network here, you would have problems, so as an example, if I created a loopback on Router 1 and configured this IP address on the loopback and then advertised that network into RIP.
show run
shows us that that that’s been changed to this. But because we’ve disabled automatic summarization, router 2 knows where both 172.16.1.0 is and 172.16.2.0.
So as an example, router 2 knows that to get to the subnet needs to send the traffic out of this interface. But to get to this subnet, it needs to send here the traffic out of this interface gigabit 0/0/0. That only works because automatic summarization has been disabled. So traffic is sent in the correct direction. Notice to get to 172.16.2.1, it’s going left and let’s send the traffic to 1.2 which is the DNS server. Traffic is going to router 3 and then to the DNS server. So that works correctly….
