HSRP for IPv6

[gfowler721]

For HSRP and IPv6, I'm toying with the idea of using the same link local on all segments along with static Globals.

FE80::1 HSRP

FE80::2 First router

FE80::3 Second router

2001:db8::1/64 HSRP

2001:db8::2/64 First Router

2001:db8::3/64 Second Router

On my 4500s, I'm unable to configure the Global for HSRP.

Comments?  Am I crazy insane?

[Nagendra Kumar Nainar]

Hi Gary,

Per my knowledge, currently this feature is not supported. I remeber trying it in 12.2(33)SRE4 which is the latest relesae for 7600 and had the same error message.

You may have to use Link local for now till the support is introduced.

HTH,

Nagendra

[gfowler721]

Not being able to set a global on the HSRP is not a big deal.   The true point of the post was to jump start a discussion about using fe80::1 for the HSRP ip on every VLAN/subnet.

[Nagendra Kumar Nainar]

Gary,

This being local to a link, I dont see any issue using same link local address as hsrp address on different interfaces.

Regards,

Nagendra

[frnkblk]

Does the use of LL break traceroutes in terms of PTRs?

[gfowler721]

No, this would not break traceroutes.   The TTL expired would source from the Interface's global IP.

[frnkblk]

Thanks for clarifying.   You're the first person to make that detail explicit.    

[gfowler721]

I'll clarify further based on RFC 3484 section 5.

The source IP of the TTL expired packet would be based on the destination IP of the original packet. 

If the source IP of the original packet, with TTL of  1, is a Global IP, and the router has a global IP on the receiving  interface, then it stands to reason that the source IP of the TTL expired  packet would then likely be the routers Global IP of the receiving  interface.

It is not likely that your host/workstation would send a packet to a Global IP with a link-local source IP.

RFC 4291:

Routers must not forward any packets with Link-Local source or destination
addresses to other links.

Anyone know of an RFC that prevents the host/node from sending a packet with a link-local source IP to a Global IP?

---

My lab has been taken over my one of my co-workers.   Can anyone test this out?

Host A - Connected to VLAN A/Subnet A (2001:db8:0:1::100/64, default gw fe80::1)

Router A, Interface A - Connected to VLAN A ( ipv6 address fe80::1 link-local)

Router A, Interface lo0 - (ipv6 address 2001:db8::1/128)

Router A, Interface B - Connected to VLAN B ( ipv6 address fe80::2 link-local, ipv6 address 2001:db8:0:2::1/64)

Host B - Connected to VLAN B/Subnet B (2001:db8:0:2::100/64, default gw fe80::2)

On Host A cli [assuming Host A is linux], 'traceroute6 -n 2001:db8:0:2::100'.

What are the results of the traceroute?

I  assume none of the TTLs would return given the lack of a Global IP on  Router A Interface A.  It wouldn't know where to sent them.   But how  about when you add a static route for 2001:db8:0:1::/64 with destination  of the physical interface 'Interface A'?

for example, 'ipv6 route 2001:db8:0:1::/64 gi1/1'.  Would this not force the router to ND for 2001:db8:0:1::100 on Interface A?   What are the results of the traceroute after adding this route?

I think this is a good exercise for understanding the nature and bounds of link-local.