IPv6 Related Question

[phiveisalive]

Good morning,

I have a problem that has me completely stumped and was hoping for some insight from those much more brilliant than I.

Here is a fast synopsis of the issue: When pinging from the ethernet side of the router, the serial interface does not pass the IPv6 traffic out. When pinging from the serial interface to another router, the destination router will not pass the IPv6 traffic through to ethernet, but it will send a reply if a ping is done to the serial interface.

Here is how the network is setup: There are 4 routers, Router A, B, and C are connected through frame-relay to router D, which is doing the frame switching. Router C has a multipoint serial subinterface with two DLCIs, routers A and B each have a single serial interface with a single DLCI. The traffic from routers A and B have to go through router C to get to each other, there is no frame route in D to shortcut going through C.

Here is the problem: If a host on router A's ethernet side sends out a ping ipv6 to router B or C, it fails. Same is true for a host on router B pinging to A or C. If a ping ipv6 from router A's serial interface is sent to router B's ethernet, it fails. Same for router B's serial to A's ethernet.

Here is what works: All ipv4 traffic..no issues at all. The serial interface of router A can ping ipv6 to the serial interface of router B. Same is true for the serial interface of router B to router A. The hosts on the ethernet side of the router can ping ipv6 to the serial interface of thier respective router.

Here is what I have checked: ip multicast-routing is enabled on all 3 routers. RIPng is passing the routes between all three routers and the ipv6 route table shows the networks from the other routers. There are zero ACLs on routers A and B. There is one on router C for NAT, but that shouldn't affect A and B since C is passing the traffic between the two of them.

I have removed all ipv4 address from all interfaces thinking it was possibly a lack of IPv6 Dual Stacking, but that made no difference either.

Attached are the configs for the 4 routers if you want to see them. I welcome any and all suggestions.

As a side note, this is an assignment for my network academy class so the hostnames, usernames, passwords, etc are not my choice.

Thank you,

Joe

[andrew.prince]

Frame-relay is Layer 2 - IPV6 is Layer 3

How do you "map" layer 2 to layer 3 in Frame-Relay?

Not only do you need to map the IPV6 address to a interface & DLCI - you ALSO need to map the IPV6 link-local address.

I suggest you choose and configure static IPV6 link-local addresses.

HTH>

[Peter Paluch · Accepted solution]

Joe,

After verifying your configuration quickly (by no means I have performed a thorough check so this is only a quick hint), I do not see IPv6/DLCI mappings for the link-local addresses created on your Frame Relay interfaces. Because there is no InverseARP for IPv6 (and you have deactivated it so or so), these mappings cannot be built automatically but have to be manually configured.

Pinging the serial interface over the Frame Relay from the router itself works because the mapping for the global unicast IPv6 address is created. Note, however, that all IPv6 IGP protocols including RIPng use link-local addresses as their next hops, and these next hops must be resolvable to Layer2 addressing. Now, your routing tables are populated with RIPng-learned routes using the link-local address of the Frame Relay interface as the next hop, and because there is no mapping in your IPv6/DLCI mapping table, sending packets through that next hop fails.

You will have to manually find out the link-local addresses of your individual Frame Relay interfaces, and create appropriate mappings manually.

Best regards,

Peter

[phiveisalive]

Mapping for the link-local was never mentioned in the class or the Cisco modules, so I am glad that you were kind enough to stop by and help out. I will make that change at lunch and clear this up.

I am curious then, without asking anyone to become a teacher here...the serial interface and the ethernet interface both have the same link-local address (I remember changing one last night in a futile attempt to figure this all out). Does it matter that they are the same or will one need to be changed in addition to the mapping?

Clearly I have a lot to learn and I know that, but having spent literally 2 days on this one issue trying to figure out what was wrong I *really* appreciate the help you provided.

Thanks,

Joe

[andrew.prince]

As soon as you enable IPV6 - the link-local is "auto" generated for you.  You just need to note it down and use it.

I really do not think that the device will have assigned the same link-local to the FastEthernet & Serial.  The link-local is auto generated using the mac-address of the interface and will start FE80:, so unless the interfaces have the same mac - the LL would have been differenet.

HTH>

[phiveisalive]

Correct, but from my understanding the serial interfaces do not have a MAC address so they borrow the ethernet interface's.

-Joe

[andrew.prince]

Correct - but something in the Link Local address would have been different!  Otherwise it woud have an an issue with it's internal DAD.

[phiveisalive]

After putting those maps in for the link-locals it worked perfectly. Thank you!

[Peter Paluch]

Andrew,

I really do not think that the device will have assigned the same 
link-local to the FastEthernet & Serial.  The link-local is auto 
generated using the mac-address of the interface and will start FE80:, 
so unless the interfaces have the same mac - the LL would have been 
differenet.

The fact is that the link-local address can and will be identical between an FastEthernet and the Serial interface in this case - the Serial does not have any MAC address and it will just borrow the first MAC address from the assigned MAC address block on the device (usually, that boils down to the first FastEthernet interface). DAD is not performed internally between interfaces as far as I know (should it be performed?). Because of its link-local scope, as long as the address is unique on a link, it is perfectly usable. There is really nothing wrong with using the same link-local address on several interfaces. It is actually very similar to using the same loopback interface with the IP Unnumbered feature on several interfaces in parallel.

You can even configure the link-local address to be the same on several interfaces manually (which is by the way in my opinion the best way to do for these Serial interfaces - instead of finding out their nearly random link-local addresses, just configure your own simple link-local address and use it on Serial interfaces and in the DLCI mappings).

Best regards,

Peter

[andrew.prince]

Thanks for the correction - the day is not wasted when you learn something new!