Best practice setting for EIGRP bandwidth?

[jmaxwellUSAF]

Hello.

I recently discovered that routing was bad because of previously configured EIGRP bandwidth settings throughout LAN.

What is best way to set vanilla EIGRP bandwidth?

What is the EIGRP default bandwidth number?

Thank you.

[MHM Cisco World]

https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/13673-14.html

Check this how you modify metric in eigrp

[David Ruess]

Hello,

Just to make sure we are talking about the same thing. There is 2 related things with BW when it pertains to EIGRP.

1. The Percentage (%) of Bandwidth (BW) used by EIGRP for control plane traffic. This has nothing to do with the routing of data packets but rather how much BW EIGRP Hello/Update/Query, etc messages are allowed to consume of the total BW.

2. The Bandwidth EIGRP uses in its metric calculation. This is a bit misunderstood sometimes as EIGRP uses only the Minimum BW along the path in its metric calculation. For example: If you have 3 10 Gig links and 1- 1Gig link and you change one of the 10Gig links to 5Gig using the BW command this will have NO affect on EIGRP as the minimum BW along the path is STILL 1 Gig. 

Best practice according to most documentation is the configure the BW to the exact link BW. If you are trying to modify routing for EIGRP either change the delay on the interfaces (since EIGPR uses the "cumulative" delay), or configure an offset-list to add metric to specific interfaces or routes.

router eigrp 1

offset-list <acl#> {in | out} <offset ammount> [interface#]

The reason you DONT want to change BW to anything other than to what it actually is is that other protocols and configurations take BW into account such as QoS and OSPF to name a couple.

Hope that helps

-David

[jmaxwellUSAF]

Thanks for the reply.

My int's are all at least 1G.

should i set...

#bandwidth 1,000,000 

?

[David Ruess]

The BW should negotiate to what the interface supports. My suggestions center around if you manually enter the Bandwidth of the interface. You shouldn't have to do that regardless.

[Joseph W. Doherty]

The common exception is links, usually non-LAN, that provide transit bandwidth less then the physical interface offers.

[jmaxwellUSAF]

RE:

"should i set...  #bandwidth 1,000,000 "

The practical problem is that someone already explicitly set these bandwidths, so I need to...

...either set a different value, or I need to reset the setting as if it was never configured. 

What do you suggest?

[Joseph W. Doherty]

Well, first, would try to determine, if possible, why they were set as they are.  As @David Ruess noted in his first reply, other "things" might use that value (including SNMP bandwidth utilization monitoring).

[MHM Cisco World]

My Opinion
remove the BW for EIGRP 
keep BW as default (interface BW)
and if you want to prefer path use delay or offset-list.

[MHM Cisco World]

BW set only when redistribute

if not redistribute then eigrp take value from interface automatic no need to set it.
if you want to modify BW I dont recommend at all

[Elliot Dierksen]

What exactly do you mean "routing was bad"? I interpret that as selecting a sub-optimal path selection. Other for service policies that reference percentages, bandwidth is only used for metric calculation. It has no impact on the rate of forwarded traffic. Bandwidth and delay are the two most common interface values I have used for influencing path selection. That is generally only something that you want to do when you have multiple paths.

[jmaxwellUSAF]

My conclusion is that my predecessor unsuccessfully tried to traffic shape. We had a real routing mess. Now that I changed a few major locations to from 500, or 20,000 or 250,000, to #bandwidth 1,000,000 , things are routing much more logically, seemingly normally.

How do I clear the bandwidth setting so it restores to its default, as if nothing was ever inserted?

[Elliot Dierksen · Accepted solution]

I think "no bandwidth X" on the interface would work, but almost certainly "default bandwidth" would do the same.