WAN BGP/OSPF/IPv6 Tunnel (Uniform 80% Packet Loss)

Unanswered Question
Oct 14th, 2009

I've been racking my brain for two days now, searching Cisco documentation, my CCNP study materials and performing various web searches and I've yet to find a cause for this odd issue.

I work for a Internet Service Provider and for testing purposes while we wait for native IPv6 backbone connectivity I've been setting up IPv6 via OSPF on our core network with a /32 we've been assigned by ARIN and testing external connectivity through a ipv6ip tunnel with Sprint set up on our Sprint backbone router. We have a BGP peering session running over the tunnel with Sprint.

We are experiencing uniform packet loss (80 percent) when pinging from routers routing through the backbone router over the tunnel to the IPv6 internet. However, when we ping from the backbone router through the tunnel to the IPv6 internet we experience no packet loss. Furthermore we can ping from our routers to the backbone router tunnel address just fine.

The backbone router is a Cisco 12K running GRP-B management and the adjacent routers/switches are Cisco 6509s running Sup720 supervisor cards.

Here is some ping examples:

The backbone router can ping ipv6.google.com just fine through the tunnel, which means the tunnel and BGP is running fine.

router.backbone.metroix#ping ipv6 ipv6.google.com

Translating "ipv6.google.com"...domain server ( [OK]

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 2001:4860:B004::68, timeout is 2 seconds:


Success rate is 100 percent (5/5), round-trip min/avg/max = 220/221/224 ms

We can ping from a adjacent router to the backbone router's local tunnel address fine:

switch.core.metroix#ping ipv6 2001:440:EEEE:FF34::2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 2001:440:EEEE:FF34::2, timeout is 2 seconds:


Success rate is 100 percent (5/5), round-trip min/avg/max = 0/0/0 ms

But when we ping from the adjacent router across the tunnel to the address on the other side or any ipv6 internet address we get the following:

switch.core.metroix#ping 2001:440:EEEE:FF34::1 repeat 20

Sending 10, 100-byte ICMP Echos to 2001:4860:B004::68, timeout is 2 seconds:

Packet sent with a source address of 2607:FD80:FFFF::1

Reply to request 0 (184 ms)

Request 1 received unknown echo response type U

Request 2 timed out

Request 3 received unknown echo response type U

Request 4 timed out

Reply to request 5 (184 ms)

Request 6 received unknown echo response type U

Request 7 timed out

Request 8 received unknown echo response type U

Request 9 timed out

Success rate is 20 percent (2/10), round-trip min/avg/max = 184/184/184 ms

The pattern of response, U, drop, U, drop, repeat does not change and packet loss to any IPv6 site is 80 percent.

We've statically assigned the adjacent routers with default routes pointing to the backbone router and the backbone router itself has a statically assigned default route pointing to the tunnel.

Here is the current configuration and default route information:

switch.core.metroix#sho ipv6 route ::/0

Routing entry for ::/0

Known via "static", distance 1, metric 0

Redistributing via ospf 10

Route count is 1/1, share count 0

Routing paths:

2607:FD80:FFFF::3 <--- Our backbone router

Last updated 15:19:06 ago

(From our backbone router)

router.backbone.metroix#sho ipv6 route ::/0

S ::/0 [1/0]

via ::, Tunnel1

This is our tunnel configuration:

interface Tunnel1

description IPv6 TO SPRINT

no ip address

no ip directed-broadcast

ipv6 address 2001:440:EEEE:FF34::2/64

tunnel source Loopback1

tunnel destination (censored)

tunnel mode ipv6ip


On the Cisco 12K backbone router, The OC-3 Uplink to Sprint is an engine 0 Card and the connection to the adjacent 6509s is on an engine 1 gig Ethernet card.

Any ideas?

I have this problem too.
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Giuseppe Larosa Wed, 10/14/2009 - 10:10

Hello Brandon,

I would say it is a CEF, or CEFv6 issue when you ping the GSR interfaces the packets are processed switched and are not sent effectively over the tunnel.

What IOS image is running on your device?

this can help for a bug search

also may you check that you have enabled CEF for ipv6 in distributed form?

Hope to help


fortino.brandon Wed, 10/14/2009 - 11:09

Hello Giuslar,

We are running IOS (tm) GS Software (GSR-P-M), Version 12.0(32)S8, RELEASE SOFTWARE (fc1).

I believe Distributed CEF for IPv6 is enabled as the command router.backbone.metr(config)#no ipv6 cef distributed results in:

Cannot disable IPv6 DCEF on this platform

Thanks in advance.


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