Groups > comp.os.linux.development.system > #461

ping to local interface v4 address works, even though it's admin/line down

Newsgroups	comp.os.linux.development.system
Date	2012-09-15 19:15 -0700
Message-ID	<26eec478-85d3-4ba9-9830-d8312eb894bc@googlegroups.com> (permalink)
Subject	ping to local interface v4 address works, even though it's admin/line down
From	anjanishp@gmail.com

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Can somebody help me understand why ping works to a local interface, even if it's admin and line protocol down in linux. 

I have a eth1 interface, i assign v4 address to it. 
I make the interface down. 
try ping to the v4 address, and ping is success. 

Please find the logs for the bahaviour. 

root@avi:/home/avinash# uname -a 
Linux avi 3.2.0-23-generic-pae #36-Ubuntu SMP Tue Apr 10 22:19:09 UTC 2012 i686 i686 i386 GNU/Linux 
root@avi:/home/avinash# 

root@avi:/home/avinash# ifconfig eth1 22.0.0.1 
root@avi:/home/avinash# ifconfig eth1 
eth1      Link encap:Ethernet  HWaddr 00:30:48:b1:ee:33   
          inet addr:22.0.0.1  Bcast:22.255.255.255  Mask:255.0.0.0 
          UP BROADCAST MULTICAST  MTU:1500  Metric:1 
          RX packets:65 errors:0 dropped:0 overruns:0 frame:0 
          TX packets:17082 errors:0 dropped:0 overruns:0 carrier:0 
          collisions:0 txqueuelen:1000 
          RX bytes:5926 (5.9 KB)  TX bytes:3841723 (3.8 MB) 
          Interrupt:44 Base address:0xe000 

root@avi:/home/avinash# route -n 
Kernel IP routing table 
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface 
0.0.0.0         10.16.48.1      0.0.0.0         UG    100    0        0 eth0 
10.16.48.0      0.0.0.0         255.255.255.0   U     0      0        0 eth0 
22.0.0.0        0.0.0.0         255.0.0.0       U     0      0        0 eth1 
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 eth0 
root@avi:/home/avinash# ifconfig eth1 down 
root@avi:/home/avinash# route -n 
Kernel IP routing table 
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface 
0.0.0.0         10.16.48.1      0.0.0.0         UG    100    0        0 eth0 
10.16.48.0      0.0.0.0         255.255.255.0   U     0      0        0 eth0 
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 eth0 
root@avi:/home/avinash# ifconfig eth1 
eth1      Link encap:Ethernet  HWaddr 00:30:48:b1:ee:33   
          inet addr:22.0.0.1  Bcast:22.255.255.255  Mask:255.0.0.0 
          BROADCAST MULTICAST  MTU:1500  Metric:1 
          RX packets:65 errors:0 dropped:0 overruns:0 frame:0 
          TX packets:17082 errors:0 dropped:0 overruns:0 carrier:0 
          collisions:0 txqueuelen:1000 
          RX bytes:5926 (5.9 KB)  TX bytes:3841723 (3.8 MB) 
          Interrupt:44 Base address:0xe000 

root@avi:/home/avinash# ping 22.0.0.1 
PING 22.0.0.1 (22.0.0.1) 56(84) bytes of data. 
64 bytes from 22.0.0.1: icmp_req=1 ttl=64 time=0.027 ms 
64 bytes from 22.0.0.1: icmp_req=2 ttl=64 time=0.019 ms 
^C 
--- 22.0.0.1 ping statistics --- 
2 packets transmitted, 2 received, 0% packet loss, time 999ms 
rtt min/avg/max/mdev = 0.019/0.023/0.027/0.004 ms 
root@avi:/home/avina

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ping to local interface v4 address works, even though it's admin/line down anjanishp@gmail.com - 2012-09-15 19:15 -0700
  Re: ping to local interface v4 address works, even though it's admin/line down Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2012-09-16 10:06 +0300

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