EIGRP Interface Metrics

[David.Duddell]

Hi Everyone,

Is there any way / command to change the default bandwidth assigned to SVI's? The issue I have is with EIGRP and the path metric calculation. With the SVI defaulting to 1Gbps any upstream EIGRP router will see the path minimum bandwidth as 1 Gbps, even though all routed links to reach that destination SVI are 10G.

I can change by configuring a bandwidth statement on the SVI interface, but was wondering if there was a way this could be set via a single command?

[Deepak Kumar]

Hi,

Since IOS 15 version Cisco support named mode for EIGRP (for IOS XR it was by default). To be short, the multiplier there is 65536 instead of 256 and the parameters are calculated a bit differently.

The old version of IOS calculating EIGRP classic metrics. Which is fit for Fast Ethernet interfaces but not for Ten GIG To solve this problem, EIGRP supports wide metrics which uses 64-bit values instead of the 32-bit values that EIGRP classics metric uses. EIGRP wide metrics supports interfaces up to 4.2 terabits and uses a different composite cost metric formula.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_eigrp/configuration/xe-3s/ire-xe-3s-book/ire-wid-met.html

https://ccieblog.co.uk/eigrp/eigrp-wide-metric-calculation

Since, If you are changing metric calculation then Cisco and everyone are recommended to play with Delay (K3). There are many disadvantages are there to play with interface bandwidth.

Regards,

Deepak Kumar

[Stephen McBride]

I have the same problem as David. Basically the problem is that by default a SVI has a bandwidth of 1g. So in my case the destination route is an SVI with a bandwidth of 1g meaning the lowest bandwidth on the path is 1G even though the whole path to that last hop is 10G. It is a pain and I think an oversight from Cisco. I think the default bandwidth of all SVIs should have been increased with the introduction of named mode to cater for this issue. 

[paul driver]

Hello

Even in named mode my understanding it shouldn't mater to a extent for path manipulation, As the default K values are still BW/Delay  So if you change the interface delay then the calculated compositic metric be it 32/64 bit will change accordingly

[Stephen McBride]

I understand that we can leverage delay but the whole point of the Wide stuff is to take into account bigger links in routing decisions. From my viewpoint it seems that it is not going to work unless we manually alter the bandwidth on all VLAN SVIs. 

[Deepak Kumar]

Hi,

I missed the point of SVI in my last reply. An SVI interface is having its default bandwidth. As our all SVIs are having the same bandwidth then I am not looking any sense to change the bandwidth of an SVI. I am not sure but there will must be some technical reason so that Cisco didn't increase bandwidth yet on SVIs. I will not play with Switch default architect If I am not sure about the pros and cons.  

Here, I am looking only sense to change the delay or use the other K values.

Regards,

Deepak Kumar