[c-nsp] IOS 15.0 ipv6-related weirdness (fails to fallback to ipv4)

[Bruce Pinsky]

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Michael Ulitskiy wrote:
> Hello,
> 
> I have a 2800 router with IOS 15.0(1)M7 with no ipv6 connectivity. There are no ipv6
> addresses configured on any interfaces and i've added:
> 
> no ipv6 cef
> no ipv6 unicast-routing
> 
> commands to config.
> 
> Nonetheless when I try to ping google the following happens:
> 
> c2800#ping google.com
> Translating "google.com"...domain server (167.206.112.138) [OK]
> 
> Type escape sequence to abort.
> Sending 5, 100-byte ICMP Echos to 2607:F8B0:4006:801::1004, timeout is 2 seconds:
> 
> % No valid source address for destination
> Success rate is 0 percent (0/1)
> 
> c2800#sh hosts 
> Default domain is aceinnovative.com
> Name/address lookup uses domain service
> Name servers are 167.206.112.138, 167.206.7.4
> 
> Codes: UN - unknown, EX - expired, OK - OK, ?? - revalidate
>        temp - temporary, perm - permanent
>        NA - Not Applicable None - Not defined
> 
> Host                      Port  Flags      Age Type   Address(es)
> google.com                None  (temp, OK)  0  IPv6   2607:F8B0:4006:801::1004
> 
> So when it sees AAAA record it tries to use it (regardless ipv6 routing has been disabled), sees 
> there're no valid ipv6 addresses to use as source and fails, instead of trying to use alternative
> ipv4 addresses. It's also very strange that only IPv6 address has been cached by resolver.
> It looks like resolver discards any A record in the presence of AAAA.
> 
> FYI:
> c2800#sh ipv6 interface brief 
> FastEthernet0/0            [up/up]
>     unassigned
> FastEthernet0/1            [up/up]
>     unassigned
> 
> c2800#sh ipv6 route
> IPv6 Routing Table - default - 1 entries
> Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
>        B - BGP, HA - Home Agent, MR - Mobile Router, R - RIP
>        I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary
>        D - EIGRP, EX - EIGRP external, ND - Neighbor Discovery
>        O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
>        ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
> L   FF00::/8 [0/0]
>      via Null0, receive
> 
> I wonder if this is a known issue, if there are any workarounds or if I'm missing something?

Is "ipv6 enable" configured on any interface at all?  What does a "show
ipv6 interfaces" say?

With ipv6-unicast routing disabled, the router will still function as an
ipv6 host if there are any IPv6 configured interfaces.  And google returns
both an A and AAAA record for google.com.

- -- 
=========
bep



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