2.3 KiB
VRRP IPv6 Interoperation with Cisco IOS/XE
On most commercial routers, IPv6 VRRP is negotiated over IPv6 Link-Local Addresses (LLAs) that are automatically generated on each router. This holds true for ArcOS, Arista, Cisco IOS/XR, and JunOS. But, IOS/XE requires explicit VRRPv6 LLA configuration.
The Root Problem
The IOS Configuration guide says
VRRPv3 for IPv6 requires that a primary virtual link-local IPv6
address is configured to allow the group to operate. After the
primary link-local IPv6 address is established on the group, you
can add the secondary global addresses.
I.e. the operator MUST configure a manual LLA, IOS/XE can not use automatically generated LLAs for VRRPv6. This is, shall we say, unusual.
JunOS and IOS/XE
To accommodate this, one could configure short form LLAs a la
Cisco IOS/XE
vrrp 2 address-family ipv6
description ipv6 vrrp
priority 80
address FE80:: primary
address 2001:418:1::1/64
and JunOS
vrrp-inet6-group 2 {
virtual-inet6-address 2001:0418:1::1;
virtual-link-local-address FE80::;
priority 100;
accept-data;
This was working for us until we added a third router into the mix.
But
ArcOS does not like the short prefix LLA. ArcOS wants either an automatically generated LLA or an explicit full LLA a la
vrrp vrrp-group 2
virtual-address [ 2001:418:1::1 ]
virtual-link-local fe80::200:5eff:fe00:202
priority 100
The Work-Around
To interoperate with all three flavors on the same LAN, the IOS/XE must be manually configured a la
vrrp 2 address-family ipv6
description ipv6 vrrp
priority 80
address FE80:: primary
address 2001:418:1::1/64
WARNING: I am not yet sure the short form LLA is correct here. We are still working on this.
The JunOS must use auto-generation, i.e. no LLA manual configuration, a la
vrrp-inet6-group 2 {
virtual-inet6-address 2001:0418:1::1;
priority 100;
accept-data;
And ArcOS must manually configure a full explicit LLA a la
vrrp vrrp-group 2
virtual-address [ 2001:418:1::1 ]
virtual-link-local fe80::200:5eff:fe00:202
priority 100
With thanks to Sukanya who figured this all out
2023.05.30