Thursday, August 28, 2014

Convergence between SVI vs Routed Interface - Cisco 3548 NXOS


Convergence of SVI vs. Routed link on a Cisco 3548 Nexus running A1.1c

Link failures were simulated by “shut” on the remote interface.

SVI – L2 VLAN

 switch#  
 2014 Aug 28 10:04:06.348524 switch %ETHPORT-5-IF_DOWN_LINK_FAILURE: Interface Ethernet1/9 is down (Link failure)  
 2014 Aug 28 10:04:06.478105 urib: "direct": 1.1.1.0/24 no more next hops  
 2014 Aug 28 10:04:06.478419 urib: 1.1.1.0/24 Deleting & Freeing  
 2014 Aug 28 10:04:06.479344 urib: "local": 1.1.1.1/32 no more next hops  
 2014 Aug 28 10:04:06.479618 urib: 1.1.1.1/32 Deleting & Freeing  
 2014 Aug 28 10:04:06.479954 urib: "broadcast": 1.1.1.255/32 no more next hops  
 2014 Aug 28 10:04:06.480215 urib: 1.1.1.255/32 Deleting & Freeing  
 2014 Aug 28 10:04:06.480542 urib: "broadcast": 1.1.1.0/32 no more next hops  
 2014 Aug 28 10:04:06.480951 urib: 1.1.1.0/32 Deleting & Freeing  
 2014 Aug 28 10:04:06.696703 urib: "am": 1.1.1.2/32 no more next hops  
 2014 Aug 28 10:04:06.697117 urib: 1.1.1.2/32 Deleting & Freeing  

Route deletion = 478419 – 348524 =  129895us


Routed link

 switch#  
 2014 Aug 28 10:07:32.508936 urib: "direct": 1.1.1.0/24 no more next hops  
 2014 Aug 28 10:07:32.509188 urib: "local": 1.1.1.1/32 no more next hops  
 2014 Aug 28 10:07:32.509561 urib: 1.1.1.0/24 Deleting & Freeing  
 2014 Aug 28 10:07:32.509732 urib: 1.1.1.1/32 Deleting & Freeing  
 2014 Aug 28 10:07:32.512789 urib: "broadcast": 1.1.1.255/32 no more next hops  
 2014 Aug 28 10:07:32.513464 urib: 1.1.1.255/32 Deleting & Freeing  
 2014 Aug 28 10:07:32.514677 urib: "broadcast": 1.1.1.0/32 no more next hops  
 2014 Aug 28 10:07:32.515005 urib: 1.1.1.0/32 Deleting & Freeing  
 2014 Aug 28 10:07:32.523539 switch %ETHPORT-5-IF_DOWN_LINK_FAILURE: Interface Ethernet1/9 is down (Link failure)  
 2014 Aug 28 10:07:32.628070 urib: "am": 1.1.1.2/32 no more next hops  
 2014 Aug 28 10:07:32.628392 urib: 1.1.1.2/32 Deleting & Freeing  

Route deletion = 509561 – 523539 =  - 13978us

I ran multiple tests and they were always the same. Looks like the Nexus removes the route from the routing table before it even realizes or outputs that the link is down, and reacts to link changes faster with a routed link vs. SVI.

In IOS carrier-delay made a difference on certain platforms but not so much on the 3548 NXOS. 

Many more articles to come so ....

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