Re: sent an invalid ICMP type 11, code 0 error to a broadcast: 0.0.0.0 on lo?

[Denis Vlasenko]

On Wednesday 06 July 2005 20:27, Richard B. Johnson wrote:
> Only the 127.0.0.0 network should be routed through the loop-back
> device.

This is the normal dose of disinformation embedded into
otherwise useful reply from Richard. Sometimes I wonder
whether he does this for fun for for some other dark
and obscure reason.

Anyway, lo is perfetly happy with packets other than 127.x.x.x
going thru it.

# ip a
1: if: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:04:23:15:ba:76 brd ff:ff:ff:ff:ff:ff
    inet 172.17.13.22/16 brd 172.17.255.255 scope global if
2: lo: <LOOPBACK,UP> mtu 16436 qdisc noqueue
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo

# ip r
172.17.0.0/16 dev if  proto kernel  scope link  src 172.17.13.22
default via 172.17.0.1 dev if

# ping -c4 172.17.13.22
PING 172.17.13.22 (172.17.13.22) 56(84) bytes of data.
64 bytes from 172.17.13.22: icmp_seq=1 ttl=64 time=0.155 ms
64 bytes from 172.17.13.22: icmp_seq=2 ttl=64 time=0.113 ms
64 bytes from 172.17.13.22: icmp_seq=3 ttl=64 time=0.122 ms
64 bytes from 172.17.13.22: icmp_seq=4 ttl=64 time=0.121 ms
--- 172.17.13.22 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3011ms
rtt min/avg/max/mdev = 0.113/0.127/0.155/0.021 ms

On the other console:

# tcpdump -nlilo
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on lo, link-type EN10MB (Ethernet), capture size 68 bytes
11:20:37.669996 IP 172.17.13.22 > 172.17.13.22: icmp 64: echo request seq 1
11:20:37.670093 IP 172.17.13.22 > 172.17.13.22: icmp 64: echo reply seq 1
11:20:38.671066 IP 172.17.13.22 > 172.17.13.22: icmp 64: echo request seq 2
11:20:38.671125 IP 172.17.13.22 > 172.17.13.22: icmp 64: echo reply seq 2
11:20:39.672327 IP 172.17.13.22 > 172.17.13.22: icmp 64: echo request seq 3
11:20:39.672389 IP 172.17.13.22 > 172.17.13.22: icmp 64: echo reply seq 3
11:20:40.681857 IP 172.17.13.22 > 172.17.13.22: icmp 64: echo request seq 4
11:20:40.681922 IP 172.17.13.22 > 172.17.13.22: icmp 64: echo reply seq 4
--
vda

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