IPv6 over frame relay

This post will look at IPv6 over frame-relay and describe some of the small things
that differ compared to IPv4 and some gotchas.

We start out with the same topology as in my previous frame-relay post.

We configure routers R1, R2 and R3 to be in the subnet 2001:CC1E:1:1::/64.
Remember that the pool of global IPv6 unicast addresses comes from 2000::/3
which means that all today legit IPv6 addresses will start with a 2 or a 3.

R1

interface Serial0/0
encapsulation frame-relay
ipv6 address 2001:CC1E:1:1::1/64
frame-relay map ipv6 2001:CC1E:1:1::2 102
frame-relay map ipv6 2001:CC1E:1:1::3 103

I won’t say much about this config as this should be known to you if you read
my previous post on frame relay. We are using a physical interface so all DLCI’s
will be available to us. The first thing to notice about IPv6 over frame relay is that
there is no inverse ARP. This means that we need static mappings or the
frame-relay interface-dlci command on point-to-point interfaces.

We configure R2 and to mix things up a bit we use a point-to-point interface.

interface Serial0/0
encapsulation frame-relay
frame-relay interface-dlci 201

Since this is a point-to-point interface there is no need for static mappings.

R3 will use a multipoint interface but not the physical interface. We will use a
static mapping.

interface Serial0/0
encapsulation frame-relay
interface Serial0/0.301 multipoint
ipv6 add 2001:CC1E:1:1::3/64
frame-relay map ipv6 2001:CC1E:1:1::1 301

When we use IPv6 we always have a link-local address assigned to all IPv6 enbabled
interfaces. This can be seen with the show ipv6 interface brief command.

R1#sh ipv6 int brief
FastEthernet0/0 [administratively down/down]
Serial0/0 [up/up]
FE80::C001:8FF:FEE0:0
2001:CC1E:1:1::1

The link-local address is calculated based on the MAC address.

R1#sh int | i bia
Hardware is Gt96k FE, address is c201.08e0.0000 (bia c201.08e0.0000)
Hardware is Gt96k FE, address is c201.08e0.0001 (bia c201.08e0.0001)

Our link-local address is based on the first MAC of this output. We want to use
an easier to remember address so we set the link local address to FE80::1 and
then the same on R2 and R3 but with ::2 and ::3.

R1(config)#int s0/0
R1(config-if)#ipv6 add FE80::1 link-local

Now it is time to do some routing. We start out with BGP. Knowing BGP is of
course a must when you are studying for the CCIE and the difference between
IPv4 and IPv6 is not that great. We need networks to announce so we create
some loopbacks on the routers.

R1

R1(config-if)#int lo0
R1(config-if)#ipv6 add 2001:CC1E:10:1::1/64

R2

R1(config-if)#int lo0
R1(config-if)#ipv6 add 2001:CC1E:11:1::2/64

R3

R1(config-if)#int lo0
R1(config-if)#ipv6 add 2001:CC1E:12:1::3/64

Don’t you just love being able to have IP addresses with CCIE in them? 😉

Time to setup BGP. We will be using AS 100 for R1 and R2. R3 will be in AS 300.

R1

R1(config)#ipv6 unicast-routing
R1(config)#router bgp 100
R1(config-router)#nei 2001:CC1E:1:1::2 remote-as 100
R1(config-router)#address-family ipv6 unicast
R1(config-router-af)#neighbor 2001:CC1E:1:1::2 activate
R1(config-router-af)#network 2001:CC1E:10:1::/64
R1(config-router-af)#exit
R1(config-router)#bgp router-id 1.1.1.1

Notice that we need to set a router-ID because we have no IPv6 addresses
configured on the routers.

R2

R2(config)#ipv6 unicast-routing
R2(config)#router bgp 100
R2(config-router)#bgp router-id 2.2.2.2
R2(config-router)#nei 2001:CC1E:1:1::1 remote-as 100
R2(config-router)#address-family ipv6 unicast
R2(config-router-af)#nei 2001:CC1E:1:1::1 activate
R2(config-router-af)#network 2001:CC1E:11:1::/64

The session comes up and we receive one prefix.

*Mar 1 10:12:46.853: %BGP-5-ADJCHANGE: neighbor 2001:CC1E:1:1::2 Up
R1#sh bgp ipv6 uni sum
BGP router identifier 1.1.1.1, local AS number 100
BGP table version is 3, main routing table version 3
2 network entries using 304 bytes of memory
2 path entries using 152 bytes of memory
3/2 BGP path/bestpath attribute entries using 372 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
Bitfield cache entries: current 1 (at peak 1) using 32 bytes of memory
BGP using 860 total bytes of memory
BGP activity 3/1 prefixes, 3/1 paths, scan interval 60 secs
Neighbor                   V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
2001:CC1E:1:1::2
                                  4 100   8                8          3      0     0         00:04:03          1

Lets see if we have reachability.

R1#sh ipv6 route 2001:CC1E:11:1::/64
IPv6 Routing Table – 6 entries
Codes: C – Connected, L – Local, S – Static, R – RIP, B – BGP
U – Per-user Static route, M – MIPv6
I1 – ISIS L1, I2 – ISIS L2, IA – ISIS interarea, IS – ISIS summary
O – OSPF intra, OI – OSPF inter, OE1 – OSPF ext 1, OE2 – OSPF ext 2
ON1 – OSPF NSSA ext 1, ON2 – OSPF NSSA ext 2
D – EIGRP, EX – EIGRP external
B 2001:CC1E:11:1::/64 [200/0]
via 2001:CC1E:1:1::2
R1#ping 2001:CC1E:11:1::2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:CC1E:11:1::2, timeout is 2 seconds:
!!!!!

Indeed we do, now lets setup peering between R1 and R3.

R1

R1(config-router)#nei 2001:CC1E:1:1::3 remote-as 300
R1(config-router)#address-family ipv6 unicast
R1(config-router-af)#nei 2001:CC1E:1:1::3 activate

R3

R3(config-router)#nei 2001:CC1E:1:1::1 remote-as 100
R3(config-router)#address-family ipv6 unicast
R3(config-router-af)#nei 2001:CC1E:1:1::1 activate

Now lets look at the BGP table on R1.

R1#sh bgp ipv6 uni
BGP table version is 12, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete
Network                                   Next Hop                         Metric    LocPrf    Weight    Path
*> 2001:CC1E:10:1::/64
                                                      ::                                   0                     32768       i
*>i2001:CC1E:11:1::/64
                                                     2001:CC1E:1:1::2
                                                                                            0        100           0           i
*> 2001:CC1E:12:1::/64
                                                     2001:CC1E:1:1::3
                                                                                            0                         0         300 i

We can see R3’s loopback, nothing weird, yet…We have a next-hop of
2001:CC1E:1:1::3 which is expected. Now look at the show ipv6 route bgp
output.

R1#sh ipv6 route bgp
IPv6 Routing Table – 7 entries
Codes: C – Connected, L – Local, S – Static, R – RIP, B – BGP
U – Per-user Static route, M – MIPv6
I1 – ISIS L1, I2 – ISIS L2, IA – ISIS interarea, IS – ISIS summary
O – OSPF intra, OI – OSPF inter, OE1 – OSPF ext 1, OE2 – OSPF ext 2
ON1 – OSPF NSSA ext 1, ON2 – OSPF NSSA ext 2
D – EIGRP, EX – EIGRP external
B 2001:CC1E:11:1::/64 [200/0]
via 2001:CC1E:1:1::2
B 2001:CC1E:12:1::/64 [20/0]
via FE80::3, Serial0/0

The route to 2001:CC1E:12:1::/64 has been resolved to a next-hop of FE80::3.
Do we have reachability to this network?

R1#ping 2001:CC1E:12:1::3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:CC1E:12:1::3, timeout is 2 seconds:
…..
Success rate is 0 percent (0/5)

No, we don’t. We don’t have a mapping for the link-local address. Debug frame-relay
packet should confirm this.

R1#debug frame-relay packet
Frame Relay packet debugging is on
R1#ping 2001:CC1E:12:1::3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:CC1E:12:1::3, timeout is 2 seconds:
*Mar 1 00:35:52.759: Serial0/0:Encaps failed–no map entry link 79(IPV6).
*Mar 1 00:35:54.767: Serial0/0:Encaps failed–no map entry link 79(IPV6).
*Mar 1 00:35:56.767: Serial0/0:Encaps failed–no map entry link 79(IPV6).
*Mar 1 00:35:58.771: Serial0/0:Encaps failed–no map entry link 79(IPV6).
*Mar 1 00:36:00.775: Serial0/0:Encaps failed–no map entry link 79(IPV6).
Success rate is 0 percent (0/5)

Indeed, there is no mapping. Lets configure this.

R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#int s0/0
R1(config-if)#frame-relay map ipv6 FE80::3 103
R1(config-if)#^Z
R1#ping 2001:CC1E:12:1::3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:CC1E:12:1::3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/37/88 ms
R1#

Success, but the question still is why do we have a link-local next-hop for
R3’s loopback interface? RFC 2545 – Use of BGP-4 Multiprotocol extensions
for IPv6 Inter-Domain Routing gives us a hint.

A BGP speaker shall advertise to its peer in the Network Address of
Next Hop field the global IPv6 address of the next hop, potentially
followed by the link-local IPv6 address of the next hop.

We must announce the global next-hop and potentially a link-local one.

The link-local address shall be included in the Next Hop field if and
only if the BGP speaker shares a common subnet with the entity
identified by the global IPv6 address carried in the Network Address
of Next Hop field and the peer the route is being advertised to.

If the BGP peers share a common subnet the link-local address shall be included.
Why doesn’t the route to R2’s loopback have a link-local next-hop?
Once again, RFC 2545 gives us the answer.

As a consequence, a BGP speaker that advertises a route to an
internal peer may modify the Network Address of Next Hop field by
removing the link-local IPv6 address of the next hop.

If announcing to an internal peer, we may modify the next-hop by removing the
link-local address. R1 and R2 are in the same AS so they are internal peers.

Now we have seen how BGP works, what about IGPs? Lets try to configure
OSPF between R1 and R2.

R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#int s0/0
R1(config-if)#ipv6 ospf 1 area 0
R1(config)#ipv6 router ospf 1
R1(config-rtr)#router-id 1.1.1.1

R2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#int s0/0.201
R2(config-subif)#ipv6 ospf 1 area 0
R2(config-subif)#exit
R2(config)#ipv6 router ospf 1
R2(config-rtr)#router-id 2.2.2.2

The peering won’t be successful, why? We turn off the route-cache and debug IPv6 packets.

R1(config)#int s0/0
R1(config-if)#no ip route-cache
R1(config-if)#^Z
R1#debug ipv6 packet
IPv6 unicast packet debugging is on
R1#
*Mar 1 08:59:20.181: IPV6: source FE80::2 (Serial0/0)
*Mar 1 08:59:20.185: dest FF02::5
*Mar 1 08:59:20.185: traffic class 224, flow 0x0, len 76+4, prot 89, hops 1, forward to ulp

Let’s try a ping to FF02::5 which is the destination address of IPv6 OSPF packets.

R1#ping FF02::5
Output Interface: Serial0/0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FF02::5, timeout is 2 seconds:
Packet sent with a source address of FE80::1
Request 0 timed out
Request 1 timed out
Request 2 timed out
Request 3 timed out
Request 4 timed out
Success rate is 0 percent (0/5)
0 multicast replies and 0 errors.

No success, we can see that the packets are source from FE80::2 which must
be mapped. Also, we must have broadcast capability on one PVC, does it matter
which one? This is output from debug frame-relay packet when doing a ping to FF02::5

R1#debug frame-relay packet
Frame Relay packet debugging is on
R1#ping FF02::5
Output Interface:
*Mar 1 09:04:41.549: Serial0/0(i): dlci 102(0x1861), pkt type 0x86DD, datagramsize 80Serial0/0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FF02::5, timeout is 2 seconds:
Packet sent with a source address of FE80::1
*Mar 1 09:04:45.349: Serial0/0: broadcast search
*Mar 1 09:04:45.353: Serial0/0:encaps failed on broadcast for link 79(IPV6)
Request 0 timed out

This shows us clearly that we have no broadcast capability. Lets look at what
frame-relay mappings we have, R2 is point-to-point only so no need for mappings there.

R1#sh run | i frame-relay map
frame-relay map ipv6 FE80::3 103
frame-relay map ipv6 2001:CC1E:1:1::3 103
frame-relay map ipv6 2001:CC1E:1:1::2 102

We don’t have a mapping for R2’s link-local address. We will need that and we
will also need broadcast capability for the PVC. To prove that we can add the
brodcast capability by configuring a map for the global address I will configure that.

R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#int s0/0
R1(config-if)#frame-relay map ipv6 FE80::2 102
R1(config-if)#frame-relay map ipv6 2001:CC1E:1:1::2 102 broad

Can we ping FF02::5 now?

R1#ping FF02::5
Output Interface: Serial0/0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FF02::5, timeout is 2 seconds:
Packet sent with a source address of FE80::1
Reply to request 0 received from FE80::2, 40 ms
Reply to request 1 received from FE80::2, 52 ms
Reply to request 2 received from FE80::2, 96 ms
Reply to request 3 received from FE80::2, 40 ms
Reply to request 4 received from FE80::2, 128 ms
Success rate is 100 percent (5/5), round-trip min/avg/max = 40/71/128 ms
5 multicast replies and 0 errors.

Looking much better now. However, there is still no OSPF peering, why?

R1#sh ipv6 ospf interface
Serial0/0 is up, line protocol is up
Link Local Address FE80::1, Interface ID 6
Area 0, Process ID 1, Instance ID 0, Router ID 1.1.1.1
Network Type NON_BROADCAST, Cost: 64

R2#sh ipv6 ospf int
Serial0/0.201 is up, line protocol is up
Link Local Address FE80::2, Interface ID 14
Area 0, Process ID 1, Instance ID 0, Router ID 2.2.2.2
Network Type POINT_TO_POINT, Cost: 64

We have a mismatch in the network types. We will set both sides to broadcast.

R1(config)#int s0/0
R1(config-if)#ipv6 ospf network broadcast

R2(config)#int s0/0.201
R2(config-subif)#ipv6 ospf network broadcast
R2(config-subif)#

And finally we have a working peering.

*Mar 1 09:16:27.185: %OSPFv3-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial0/0.201 from LOADING to FULL, Loading Done

I hope this post has cleared some misconceptions about IPv6 over frame relay.
If you have any questions please post them in the comments section.
You can find the final configs for this lab here. You can find the topology for GNS3
in my earlier post on frame-relay.