altering EIGRP administrative distance that is advertized

[jrhofman]

Is there anyway to config a router to alter the AD that it advertizes out it's interfaces. I need to change the distance from 90 to 170 to match external EIGRP routes?

If this is possible will a router that gets an External EIGRP route (170) and an Internal EIGRP route (170) treat them equal and use the delays to detirmine which is the best path?

[d_pinto]

You can change the AD using the distance command once in routing config mode....

cisco#

cisco# config t

cisco(config) router eigrp xxx

cisco (config-router)#distance eigrp xxx xxx

in your case to make them the same you would use

cisco (config-router)#distance eigrp 170 170

Now before you go ahead and do that I would test this out in a lab environment to make sure it does what you are looking to do.... Messing with the AD can cause some serious routing issues.

As to your second question... with the AD's being the same eigrp will use other metrics to determine the best path.

Here is an snip from designing large scale ip networks. A link is to the page is also provided below. You may need a CCO account to access the content....

***************************************************

Routing protocols compare route metrics to select the best route from a group of possible routes. The following factors are important to understand when designing an Enhanced IGRP internetwork. Enhanced IGRP uses the same vector of metrics as IGRP. Separate metric values are assigned for bandwidth, delay, reliability, and load. By default, Enhanced IGRP computes the metric for a route by using the minimum bandwidth of each hop in the path and adding a media-specific delay for each hop. The metrics used by Enhanced IGRP are as follows:

* Bandwidth—Bandwidth is deduced from the interface type. Bandwidth can be modified with the bandwidth command.

* Delay—Each media type has a propagation delay associated with it. Modifying delay is very useful to optimize routing in network with satellite links. Delay can be modified with the delay command.

* Reliability—Reliability is dynamically computed as a rolling weighted average over five seconds.

* Load—Load is dynamically computed as a rolling weighted average over five seconds.

When Enhanced IGRP summarizes a group of routes, it uses the metric of the best route in the summary as the metric for the summary.

*****************************************************

So with AD's being the same you should be able to adjust the routing with the delay and bandwidth statements which are configurable on a per interface basis...

http://www.cisco.com/en/US/customer/tech/tk365/tk207/technologies_tech_note09186a0080094823.shtml

http://www.cisco.com/univercd/cc/td/doc/cisintwk/idg4/nd2003.htm#38330

[jrhofman]

I believe the EIGRP command you refer to has to be applied to routers that are "recieving" the updates rather than the router that is sending them (if i read things correctly). While this would probably work it requires me to touch a lot of routers. I was hoping to change it only in the router that is sending the updates.

[mark-obrien]

AD is not advertised with any routing protocol.

[jrhofman]

I must be missing something major here. If I do a show ip ro on a router and some routes (external EIGRP) have an administrative distanced of 170 and other routes (internal EIGRP) have a distance of 90, how is the router (that I do the show route on) geting these different metrics?

[cgregg]

The External EIGRP routes are routes external to your EIGRP AS which are being injected somewhere by a router with one interface in the EIGRP network and one in something different than EIGRP. Which the default AD for External EIGRP routes is 170.

internal EIGRP routes have a default AD of 90 and these routes are learned by neighboring EIGRP routers with in the same AS.

[jrhofman]

understood. So it's the "receiving" router that ultimately calculates the distance of the routes it receives.

.

[Harold Ritter]

The receiving router doesn't calculate the administrative distance. The AD is a value assigned to the route depending on what RP we learn it from to determine its level of preference in relation to routes received from other RPs. Here's a list of AD per protocol:

connected 0

static 1

eigrp summary route 5

bgp 20

eigrp internal 90

igrp 100

ospf 110

isis 115

rip 120

eigrp external 170

bgp internal 200

Hope this helps,