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Distance command in Cisco IOS

Dear group,

I am an MSc student in Electrotechnical Engineering and I am currently researching configuration commands in Cisco IOS for my thesis.

In particular, I am interested in setting the administrative distance of a route according to the route's destination prefix. I am aware of the "distance" command in the form:

distance {ip-address {wildcard-mask}} [ip-standard-list] [ip- extended-list]

which allows one to set the administrative distance of a route (within the configuration of a particular routing protocol) according to what Cisco's documentation [1] refers to as the "source of a route". The documentation is not very clear on what this means, but my interpretation is that it refers to the neighboring router from which the route in question was received. On the other hand, the book "Cisco IOS in a nutshell" says it refers to the route's destination address; confusingly, it also describes the command's syntax as

distance distance [address mask] [access-list]

which is missing one argument relative to the version above.

Since the two sources contradict each other, I wonder if you could provide me an answer to any of the following questions:

(i) What is the correct syntax of the "distance" command and, in particular, what do the ip-address and wildcard-mask parameters mean; (ii) Is there any way, using this command or another one, to set a route's administrative distance based on the route's destination prefix/address?

Thanks in advance.

Best regards, Tiago

[1] Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols, Release 12.2
Reply to
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The syntax for the distance command is

distance {ip-address {wildcard-mask}} [ip-standard- list]| [ip-extended-list]

example: distance 150 10.1.1.0 0.0.0.255

This distance command should not be confused with route metrics that are used by the various routing protocols - RIP, EIGRP, OSPF, ISIS, etc

Reply to
Merv

You can change the admin distance of a routing protocol with the command:

distance xxx

this will affect all routes heard by the protocol.

You can get more granular by doing this:

distance xxx 0.0.0.0 255.255.255.255 99

With 99 being an access list that identifies a destination network.

The change in admin distance will only affect routes towards the destination in access list 99, recieved from any router.

Additionally, you can change the admin distance from a specific route source: distance xxx 10.1.1.1 0.0.0.0

This will cause a change in consideration for route heard from that specific source.

And again, more granular:

distance xxx 10.1.1.1 0.0.0.0 99

This will affect the consideration only for routes identified in ACL 99, but they must come from router sourse 10.1.1.1

HTH

Reply to
John Agosta

Thanks, that's precisely what I wanted to know.

Best regards, Tiago

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