Bandwidth, VLANs, and 10 G Links

Peter Welcher
Architect, Operations Technical Advisor

In the middle of a deployment, Jim Marinelli and I discovered a small surprise (to us, anyway). Recent SXH or SXI code, possibly VSS in the mix. (I’d like to have narrowed it down further for you, but there’s been no time to do testing of various variations.)

Jim saw that OSPF wasn’t using the direct 20 G etherchannel crosslink between two switches. The switches are ASBR’s between two OSPF domains, so we ran two VLANs across the crosslink, to allow OSPF adjacencies within each OSPF domain (We do the same thing with ABR’s: have one link or VLAN on each “side of the border” to prevent potential odd routing paths, especially under failure conditions.)

Upon investigation, the bandwidth for the VLAN SVI interfaces was 1 Gbps, where we’d have expected them to inherit 20 Gbps. 

Setting the bandwidth manually resolved the problem. 

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