From: Chuck Larrieu (chuck@xxxxxxxxxxxxx)
Date: Mon Jan 08 2001 - 23:35:33 GMT-3
I'm looking at the outputs of a number of show ip route commands in the
Slattery/Burton book. I wish I could say that what I am seeing is logical,
and unified. It's not. It seems to depend upon the routing protocol in
questions, the address itself ( prefix length ) and such variables as
metric. I see printed examples here of more specific routes appearing before
connected, or after.
I don't have enough outputs in front of me to be certain, but it also
appears that interface number may be a factor. For example, in some of the
prints, the order "appears" to be loopback, ethernet, serial.
Chuck
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
frank wells
Sent: Monday, January 08, 2001 12:15 PM
To: ccielab@groupstudy.com
Subject: Re: routing table question
The router puts all directly connected routes in first because it finds
those quickest. It will then add the static routes followed by routes
learned via a routing protocol. Routes are given an administrative distance
(weight) depending on the routing protocol they were learned from.
Administrative Distance is used to choose the most trustworthy routing
protocols' route over other less trustworthy routing protocols. See Later.
What it advertises is a whole different discussion...
When performing a route lookup, it uses the following ordered criterion to
determine the best route to the destination network:
1 Host address
2 A subnet
3 A group of subnets (summary route etc)
4 A major network address
5 A group of major network addresses (supernet)
6 Default route or network etc
For administrative distance, the route with the lowest weight will
ordinarily be the one added to the route table:
Table:
Connected Interface 0
Static Route 1
Eigrp Summary Route 5
External BGP 20
Eigrp 90
IGRP 100
OSPF 110
IS-IS 115
RIP 120
EGP 140
External Eigrp 170
Internal BGP 200
Unknown 255
Pick up a copy of Routing TCP/IP by Jeff Doyle. It rules.
>From: David M Anderson <dma@cisco.com>
>Reply-To: David M Anderson <dma@cisco.com>
>To: ccielab@groupstudy.com
>Subject: routing table question
>Date: Mon, 08 Jan 2001 11:34:22 -0800
>
>I thought I would include a subject line this time...
> >Date: Mon, 08 Jan 2001 11:32:27 -0800
> >To: ccielab@groupstudy.com
> >From: David M Anderson <dma@cisco.com>
> >
> >I have a real simple question that I just don't seem to see the answer
>to. In which order are routes added to a routing table? I have tried to
>see if it is metrics, routing protocol, order learned.....etc. It seems to
>be the order learned, but I am not sure about that. Can anyone clarify?
> >
> >Thanks,
> >David
>
>David Anderson
>Lab Engineer
>(408) 853-5515
>dma@cisco.com
>
> | |
> :|: :|:
> :|||: :|||:
> .:|||||||:..:|||||||:.
>C I S C O S Y S T E M S
>
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