[j-nsp] Logical Tunnels & IPv6

[Chuck Anderson]

On Sun, May 30, 2010 at 05:21:03PM -0400, Mark Kamichoff wrote:
> I just ran into what looks like an interesting limitation with 
> logical tunnels on JUNOS.  It seems that using logical tunnels with 
> an encapsulation type of ethernet results in the inability to use 
> IPv6 on such interfaces.

Yes, and I believe the reason why this is the case is because 
logical-tunnels use the same MAC address on each end.  Since IPv6 uses 
the MAC address to generate the link-local address by default, that 
may be why they prevent you from configuring inet6 on lt.

For another interesting case, if you create a l2circuit or l2vpn using 
logical tunnel interfaces from the same tunnel PIC on both ends of the 
l2circuit/l2vpn (say in a lab environment where all the routers are 
logical systems on one physical router), you will run into ARP issues 
because both ends use the same MAC address.  Both CE's will 
continually ARP for the other CE, but they will both ignore each 
other's ARP requests because they come from their "own" MAC.  You can 
work around this by using static ARP entries that point to the same 
MACs on each end, which "shouldn't" work but it does...IP traffic 
passes fine despite the fact that there is a duplicate MAC on the 
CE-CE subnet.  I haven't tried family inet6 here though.

l2circuit from CE:c1 on PE:r4 to CE:c2 on PE:r6.

PE:r4 to CE:c1:

lab at main# show logical-routers r4 interfaces lt-1/3/0 unit 58    
description "r4:fe-0/0/0.600 to c1";
encapsulation vlan-ccc;
bandwidth 100m;
vlan-id 600;
peer-unit 59;

lab at main# show logical-routers c1 interfaces lt-1/3/0 unit 59    
description "c1 to r4:fe-0/0/0.600";
encapsulation vlan;
vlan-id 600;
peer-unit 58;
family inet {
    address 192.168.16.1/24 {
        arp 192.168.16.2 mac 00:90:69:bc:2c:db;
    }
}

PE:r6 to CE:c2:

lab at main# show logical-routers r6 interfaces lt-1/3/0 unit 56 
description "r6:fe-0/1/3.600 to c2";
encapsulation vlan-ccc;
bandwidth 100m;
vlan-id 600;
peer-unit 57;

lab at main# show logical-routers c2 interfaces lt-1/3/0 unit 57    
description "c2 to r6:fe-0/1/3.600";
encapsulation vlan;
vlan-id 600;
peer-unit 56;
family inet {
    address 192.168.16.2/24 {
        arp 192.168.16.1 mac 00:90:69:bc:2c:db;
    }
}