Category: ASR

OTV FHRP filtering on a ASR router

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We configured a OTV DCI in my previous post and it was working as expected and by design. But during testing of all the VLANs I discovered a problem with HSRP over OTV, but only for 1 specific VLAN. The test results:

  • A ping from a host in DC1 in VLAN 10 to the HSRP address gives random drops
  • A ping from a host in DC1 in any VLAN to the HSRP address pings without any problems
  • Shutdown the SVI of VLAN 10 in DC2, A ping from a host in DC1 in VLAN 10 to the HSRP address without any problems
  • VLAN 10 is still disabled in DC2, but a host can ping the HSRP address from DC2 to DC1. This should be impossible because of the FHRP filtering
  • Changing the standby group number (they are the same in DC1 and DC2 to keep the same MAC address) partially solved the problem, but some hosts in DC1 got the HSRP MAC of DC2 in the ARP table. This is not what we want.
  • Moving the SVI from a 6500 switch to a 3750 switch in DC1, none of the above problems

I still have no idea why this problem only exists for VLAN 10, all other VLANs work as expected but I’ve found a good workaround for this in the configuration guide:
http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/wan/command/wan-cr-book/wan-m1.html#wp3953249580
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Configuring OTV on a Cisco ASR

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During a project I’ve been working on, we needed to configure OTV on a Cisco ASR. I did write a blog for configuring OTV on a Nexus 7000 before (click here) but the configuration on a Cisco ASR router is a bit different. The used technologies and basic configuration steps are equal, but the syntax is different for a few configuration steps .
Unfortunately, the documentation is not as good as for the Nexus 7000. I’ve found one good configuration guide (here) but this guide isn’t covering all. So, it’s a good reason to write a blog post about the basic OTV configuration on a Cisco ASR router.
For more information about OTV, check this website.
First, the network layout for this OTV network.
OTV Network layout
 
As you can see in the diagram, the ASR routers are back-to-back connected. There is no guideline how to connect these routers, as long as there is IP connectivity between them with multicast capabilities and a MTU of atleast 1542 btyes.
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