From: Scott M Vermillion (scott_ccie_list@it-ag.com)
Date: Wed Feb 04 2009 - 15:42:41 ARST
Hey Jason,
No worries man! RIP is an oddball in this way but I guess kind of being the
original IP IGP, it's well within its rights to do so. Really, when you
think about the differences between pure distance vector and a link-state
protocol, it all kinda makes sense. With a hop-count, it's really a coin
toss as to whether or not the advertising router or the receiving router
does the incrementing; either way, it's just the addition of a single hop to
the existing total hop count to reflect that link that exists between the
two routers. With something like OSPF, the cost to reach a network "one
hop" (better term in this case would likely be "one OSPF-speaker") away is
the sum of:
[the cost that next OSPF-speaker has to reach the network in question] +
[the local router's cost to reach that next OSPF-speaker].
Problem with following RIP's lead here would be that the local router's cost
to reach the next OSPF-speaker is not known by that next OSPF-speaker. It's
not just a single hop away; it's some value determined by the reference BW
configured on the local router, the BW statement on the interface pointing
to the next hop, etc. So only the local router can accurately increment
cost when we're not dealing simply with a true hop count.
I think that makes sense.
Regards,
Scott
From: Jason Morris [mailto:mcnever@gmail.com]
Sent: Wednesday, February 04, 2009 10:23 AM
To: Scott M Vermillion
Cc: Han Solo; Cisco certification
Subject: Re: Rip route generation
Thanks for the correction.
the sad thing is i actually did lab it up and just did the debug on the
receiving side... now that i'm looking at the sending side as well i can see
the advertising host is sending it with an unreachable metric.
Again thanks for the correction and keeping from infecting the minds of
others ;)
On Tue, Feb 3, 2009 at 4:09 PM, Scott M Vermillion
<scott_ccie_list@it-ag.com> wrote:
Hey Jason,
RIP is unique in that a RIP-speaker tells its neighbors what their metric
should be. Therefore, RIP-speakers do *not* increment the metric inbound.
This is a good one to lab up so that it sticks in your brain!
Regards,
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Jason Morris
Sent: Tuesday, February 03, 2009 1:26 PM
To: Han Solo
Cc: Cisco certification
Subject: Re: Rip route generation
yes it will advertise it, but the router that receives it will increment the
metric by 1 (15+1=16)and it will see the router as unreachable and not put
it in its routing table.
to advertise a 'summary-address' there has to be some part of that summary
in the RIP process for the summary to be advertised. that doesn't mean you
need a network statement, it just has to be in the process.
But yeah i'd take ALL's advice... Lab it up...
On Tue, Feb 3, 2009 at 1:39 PM, Han Solo <emaillists@me.com> wrote:
> If you have a rip learned prefix with a metric of 15 in my local ip
routing
> table will the device advertise it ? So if I issue the command
>
> "show ip route rip"
>
> and I see a 0/0 default route learned from a rip speaker , with a metric
of
> 15 will I advertise this to my other rip interfaces , I am going to say
yes
> ??
>
>
>
> On Feb 3, 2009, at 10:25 AM, Han Solo wrote:
>
> Rip can generate a 0/0 route without having a 0/0 already in it's routing
>> table , can it do this same thing for say summary routes assume the
>> following:
>>
>> router rip
>> version 2
>> net 176.1.0.0
>> no auto-summary
>>
>> interface f0/0
>> ip summary-address rip 176.1.0.0 255.255.0.0
>> ip summary-address rip 150.1.0.0 255.255.0.0
>>
>>
>> So will rip advertise that summary , even though it is not under the rip
>> process as an advertised network ?
>>
>>
>> Han Solo
>> May the force be with you
>>
>>
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>>
>>
> Han Solo
> May the force be with you
>
>
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>
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