From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Sun Feb 20 2005 - 21:40:34 GMT-3
Paste the "show ip protocols" and "show ip route" output from both R1
and R3.
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
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> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> anantha S
> Sent: Sunday, February 20, 2005 4:15 PM
> To: Cisco certification
> Subject: RIP v1 and v2 question
>
> Hi all,
>
> Question about Rip v1 router accepting a route of different mask from
> the received interface which has same major network.
>
>
> Topology:
> ----------------
> 10.50.13.128/27-------R1 (rip v1)-----10.50.13.0/28------R3 (rip
> v2)---10.50.31.0/24
>
>
> Should R1 learn 10.50.31.0/24 ?
>
> Some reason R1 is learning the route. Can someone give me the reason
?
> I thought it should check for the major network and mask in R1
> against 10.50.31.0/24 versus 10.50.13.0/28 and it should reject the
> update.
>
>
> Below are the snippet i read ((i think its specific to rip version
1))
>
------------------------------------------------------------------------
-- > -------------------- > > Send Updates > ------------------------ > Before Router 1 sends updates to Router 2, it checks the following: > b" Is the subnet information part of the same major net as the > interface that is sourcing the update? > o No. Router 1 summarizes at the major net boundary and advertises the > network. > o Yes. Does the network have the same subnet mask as the interface > that is sourcing the update? > o' No. Router 1 drops the network, and does not advertise it. > o' Yes. Router 1 advertises the subnet. > > > Receive Updates > --------------------------- > When RIP or IGRP receive an update, they perform certain checks before > accepting the update and applying the subnet mask. Below is the > sequence of events that occurs before Router 2 accepts an update from > Router 1: > b" Is the subnet received in the update on the same major net as the > interface that received the update? > o Yes. Router 2 applies the mask of the interface that received the > update. If the advertised network has a host bit set in the host > portion of the update, Router 2 applies the host mask (/32). In the > case of RIP, it continues to advertise the /32 route to the subsequent > router, but IGRP does not. > o No. Do any subnets of this major net already exist in the routing > table, known from interfaces other than the one that received the > update? Note that the network in this update should be a major net > unless the link between the two routers is an unnumbered link, in > which case it is possible for the update to contain subnet > information. > o' Yes. Router 2 ignores the update. > o' No. Router 2 applies a classful mask. If the update came across an > unnumbered link and contains subnet information (bits in subnet > portion of network are set), then Router 2 applies a host mask. Please > refer to Understanding and Configuring the ip unnumbered Command for > unnumbered case examples. > >
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