Re: source addr. for icmp if link-local-only on interface

Indeed, what I have seen. It starts with the loopbacks and there it starts
with the lowest. If there are no loopbacks, he takes the other interfaces.
That's at least what I have seen but personally I think this is not good.
Instead of just "misusing" the address of another interface, I would rather
display an error like "no global scoped ipv6 address configured". Then I
still have the possibility to specify a source address, like with v4.
To me it is just curious that this behavior is not specified (or I did not
find it) because from a routing point of view, link local is sufficient and
therefore one or the other will focus this issue...

Regards

Roger #23543
On Sep 2, 2011 1:03 PM, "garry baker" <baker.garry_at_gmail.com> wrote:
> Is this what you mean? see output below for my test of what i think you
are
> talking about...
>
> it appears to pick the lowest IPv6 address for this, dont know about the
RFC
> or Cisco implentation where this rule is coming from...
>
> the ipv4 "rule" was it used the ip address closet to the destination to
> source this packet when you did the ping from the router, unless of course
> you specify the source interface
>
>
>
> R1(config-if)#do ping 2002:2222::2 r 1
> Type escape sequence to abort.
> Sending 1, 100-byte ICMP Echos to 2002:2222::2, timeout is 2 seconds:
> .
> Success rate is 0 percent (0/1)
>
> R2#debug ipv6 packet access-list ICMP detail
> IPv6 unicast packet debugging is on (detailed) for access list ICMP
> R2#
> *Mar 1 00:20:58.635: IPV6: source 2444:4444::4 (Serial0/0)
> *Mar 1 00:20:58.635: dest 2002:2222::2
> *Mar 1 00:20:58.635: traffic class 0, flow 0x0, len 100+4, prot 58,
> hops 64, forward to ulp
> *Mar 1 00:20:58.639: IPV6: source 2002:2222::2 (local)
> *Mar 1 00:20:58.639: dest 2444:4444::4
> *Mar 1 00:20:58.639: traffic class 0, flow 0x0, len 100+4, prot 58,
> hops 64, Route not found
>
>
> R1(config-if)#int loop4
> R1(config-if)#shut
> R1(config-if)#int loop4
> *Mar 1 00:22:15.835: %LINK-5-CHANGED: Interface Loopback4, changed state
to
> administratively down
> *Mar 1 00:22:16.835: %LINEPROTO-5-UPDOWN: Line protocol on Interface
> Loopback4, changed state to down
> R1(config-if)#do ping 2002:2222::2 r 1
> Type escape sequence to abort.
> Sending 1, 100-byte ICMP Echos to 2002:2222::2, timeout is 2 seconds:
> .
> Success rate is 0 percent (0/1)
>
> R2#
> *Mar 1 00:22:18.999: IPV6: source 2555:5555::5 (Serial0/0)
> *Mar 1 00:22:19.003: dest 2002:2222::2
> *Mar 1 00:22:19.003: traffic class 0, flow 0x0, len 100+4, prot 58,
> hops 64, forward to ulp
> *Mar 1 00:22:19.003: IPV6: source 2002:2222::2 (local)
> *Mar 1 00:22:19.003: dest 2555:5555::5
> *Mar 1 00:22:19.003: traffic class 0, flow 0x0, len 100+4, prot 58,
> hops 64, Route not found
>
> R1(config-if)#no shut
> R1(config-if)#int f0/0
> R1(config-if)#no shut
> R1(config-if)#
> *Mar 1 00:23:01.319: %LINK-3-UPDOWN: Interface Loopback4, changed state to
> up
> *Mar 1 00:23:02.319: %LINEPROTO-5-UPDOWN: Line protocol on Interface
> Loopback4, changed state to up
> R1(config-if)#
> *Mar 1 00:23:04.787: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed
> state to up
> *Mar 1 00:23:05.787: %LINEPROTO-5-UPDOWN: Line protocol on Interface
> FastEthernet0/0, changed state to up
> R1(config-if)#do ping 2002:2222::2 r 1
> Type escape sequence to abort.
> Sending 1, 100-byte ICMP Echos to 2002:2222::2, timeout is 2 seconds:
> !
> Success rate is 100 percent (1/1), round-trip min/avg/max = 44/44/44 ms
> R2#
> *Mar 1 00:23:19.951: IPv6: Sending on Serial0/0
> *Mar 1 00:23:20.303: IPV6: source 2001:1111::1 (Serial0/0)
> *Mar 1 00:23:20.303: dest 2002:2222::2
> *Mar 1 00:23:20.303: traffic class 0, flow 0x0, len 100+4, prot 58,
> hops 64, forward to ulp
> *Mar 1 00:23:20.307: IPv6: nexthop FE80::1,
> *Mar 1 00:23:20.307: IPV6: source 2002:2222::2 (local)
> *Mar 1 00:23:20.307: dest 2001:1111::1 (Serial0/0)
> *Mar 1 00:23:20.307: traffic class 0, flow 0x0, len 100+4, prot 58,
> hops 64, originating
>
>
> ROUTER CONFIGS for TEST:
>
> hostname R1
> !
> ipv6 unicast-routing
> !
> interface Loopback0
> ip address 1.1.1.1 255.255.255.0
> !
> interface Loopback4
> no ip address
> ipv6 address 2444:4444::4/64
> !
> interface Loopback5
> no ip address
> ipv6 address 2555:5555::5/64
> !
> interface Loopback6
> no ip address
> ipv6 address 2666:6666::6/64
> !
> interface FastEthernet0/0
> no ip address
> shutdown
> duplex auto
> speed auto
> ipv6 address 2001:1111::1/64
> ipv6 ospf 1 area 1
> !
> interface Serial0/0
> no ip address
> ipv6 address FE80::1 link-local
> ipv6 ospf 1 area 0
> clock rate 2000000
> !
> ipv6 router ospf 1
>
>
> hostname R2
> !
> ipv6 unicast-routing
> !
> interface Loopback0
> ip address 2.2.2.2 255.255.255.0
> !
> interface FastEthernet0/0
> no ip address
> duplex auto
> speed auto
> ipv6 address 2002:2222::2/64
> ipv6 ospf 1 area 2
> !
> interface Serial0/0
> no ip address
> ipv6 address FE80::2 link-local
> ipv6 ospf 1 area 0
> clock rate 2000000
> !
> ipv6 router ospf 1
> !
> ipv6 access-list ICMP
> permit icmp any any
>
>
> --
> Garry L. Baker
>
> "With sufficient thrust, pigs fly just fine..." - RFC 1925
>
>
>
> On Fri, Sep 2, 2011 at 11:58 AM, Roger Pfaeffli <rpf23543_at_gmail.com>
wrote:
>
>> Hi group,
>>
>> On a router, if I have on a WAN link just the ipv6 link local address
>> ('cause this is enough for routing) and I execute a v6ping to a global
>> scoped address somewhere in this WAN, my router chooses a global
>> scoped address, borrowed from another interface of my router. That's
>> at least what I've tested.
>> How is this "borrowed" address chosen and where is this specified? I
>> could not find an rfc describing exactly this. I guess this is vendor
>> specific, if so, is there a documentation from Cisco explaining this?
>>
>> regards
>>
>> Roger #23543
>>
>>
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>>
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Received on Fri Sep 02 2011 - 16:11:31 ART