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Question about HSRP with IPv6 and link-local addresses

Hi all,

This may be a silly question, but how do you configure HSRP with a link-local IP address? The switches that I'm working with are 6509s running IOS version12.2(33)SXI3 (so they don't support using a global IPv6 address as the standby IP).

This is what my config looks like so far:

(ipv6 unicast-routing is configured globally)


interface Vlan649

description *** IPv6-Test-Vlan ***

no ip address

no ip redirects

no ip proxy-arp

ipv6 address ...::2/80

standby version 2

standby 1000 ipv6 autoconfig

standby 1000 timers 5 15

standby 1000 priority 250

standby 1000 preempt

standby 1000 authentication ....

The other switch in the pair is configured the same way, with an IP of ::3/80

I also configured a static route of ipv6 route ...::/80 Vlan649 <auto configured link-local address>, though I'm not sure that's necessary (and basic IPv6 connectivity works without it).

I then took a test Windows client, connected directly to switch #1, and configured it with an IP of ...::4/80. At this point basic connectivity worked. The problem that I had is when I started testing HSRP:

First, I tried to put a default gateway on the client of the auto-configured link-local address, but it would not accept it (I tried adding it through the GUI and through netsh). When I started digging deeper I found it was already there with a metric of 256. I'm not sure if it auto-discovered it or if it took the route I added even though it said it didn't. I also had a route to ....::/80 with a metric of 8, and a route to ...::4/128 with a metric of 256.

Basic connectivity still worked, but it is not using the link-local address as the next hop. If I shut down vlan 649 on switch #1 traffic dies. At first I thought it was an issue with the Windows test client, but I then I noticed that I get a routing loop when I do a trace route to the test client from outside the lab. The trace hits switch #1 and then forwards the data back to the corporate router that it got the packet from, then back to switch #1, etc.

If it were just the Windows client not working then I would think the problem lies there, but the routing loop makes me think the switch config might be missing something. I've followed the steps in http://www.cisco.com/en/US/docs/ios-xml/ios/ipv6/configuration/15-2mt/ip6-fhrp.html but I'm not making any progress. Any help is appreciated!

Sorry if this is a pretty basic issue...I'll be the first to admit that I'm an IPv6 newb

Thanks,

Josh

Everyone's tags (3)
5 REPLIES
Silver

Re: Question about HSRP with IPv6 and link-local addresses

You shouldn't manually assign Link-Local address as a default route on a client device. You may even not need any default route for IPv6. It will be learned automatically via periodic RAs.

You may take a peek at this RFC

Thanks.



Community Member

Question about HSRP with IPv6 and link-local addresses

Hi Rais,

Thanks for the feedback. I actually tried it first without using either a static link-local route on the client or a static route on my switches. When it wouldn't work I tried adding the route on the client, and then on the switch.

The main reason that I tried0 adding the route on the switch was because when I shut down one of the vlans it starts routing traffic back out to the main corporate network instead of to my test client. It should be sending the traffic to switch #2 and then on to the client (we have quite a few IPv4 VLANs configured with HSRP on these same switches and I don't have a problem with them).

The virtual MAC is 0005.73a0.03e8, so this version of IOS isn't following the RFC you linked. Very interesting.

Thanks,

Josh

Silver

Question about HSRP with IPv6 and link-local addresses

Router Advertisement [RA] is a mechanism to find the next hop router on a given link. Routers still must learn about all the networks via dynamic/static means.

HSRP for IPv4 uses a MAC address of 0000.0c07.acXX.

VRRP for IPv4 uses multicast MAC address of 00-00-5E-00-01-XX

So they can use different addresses for IPv6. HSRP is Cisco proprietary. This link talks about vrrp configuration on XR routers.

Thanks.

Community Member

Question about HSRP with IPv6 and link-local addresses

Hi Rais,

I understand all of that, but that doesn't answer the question of why it's not working with IPv6. My point with IPv4 was only that these two switches I'm testing with have HSRP working fine with v4, but not with v6 (using the exact same configuration, the way Cisco shows it should be done). I must be missing something, but I'm not sure where.

Thanks,

Josh

Community Member

Question about HSRP with IPv6 and link-local addresses

To solve this issue, I configured the Default gateway (::1) as secondary IPv6 address of ::2 and ::3, and it's working fine.

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