Dual IP address on a Server - Unable to ping or tracerout both IP addresses

[astanislaus]

The following traceroutes were done from a Cisco 1603 router whose IP addresses are as follows to a Unix Server which has 2 x IP addresses 10.11.137.21 and 10.11.137.28.

The traceroutes fail when the Unix Server has 2 x IP Addresses, but passes when one IP address is removed from the Unix Server's configuration.

duval-h#sho ip int brief

Interface IP-Address OK? Method Status Protocol

BRI0 unassigned YES unset up up

BRI0:1 unassigned YES unset up up

BRI0:2 unassigned YES unset up up

Dialer1 10.13.254.79 YES unset up up

Ethernet0 10.13.79.1 YES NVRAM up up

Loopback0 10.13.254.79 YES NVRAM up up

Virtual-Access1 unassigned YES unset up up

Failing Traceroutes when the Unix Server has 2 x IP Addresses:

----------------------------------------------------------------------------------------

duval-h#traceroute 10.11.137.21

Type escape sequence to abort.

Tracing the route to mail.benvenue-p.schools.nsw.edu.au (10.11.137.21)

1 itbr12lo1.schools.nsw.edu.au (10.23.250.2) 40 msec 40 msec

itbr21.schools.nsw.edu.au (10.23.254.221) 36 msec

2 itbr21.schools.nsw.edu.au (10.23.254.221) 40 msec 40 msec

benvenue-p.net.det.nsw.edu.au (10.11.254.137) 72 msec

3 benvenue-p.net.det.nsw.edu.au (10.11.254.137) 76 msec 80 msec *

4 * * *

5 * * *

6 * * *

7

duval-h#traceroute 10.11.137.30

Type escape sequence to abort.

Tracing the route to web1.benvenue-p.schools.nsw.edu.au (10.11.137.30)

1 itbr12lo1.schools.nsw.edu.au (10.23.250.2) 40 msec 40 msec

itbr21.schools.nsw.edu.au (10.23.254.221) 40 msec

2 itbr21.schools.nsw.edu.au (10.23.254.221) 40 msec 44 msec

benvenue-p.net.det.nsw.edu.au (10.11.254.137) 72 msec

3 benvenue-p.net.det.nsw.edu.au (10.11.254.137) 76 msec 80 msec *

4 * * *

5 * * *

6 *

Passing Traceroute when one IP Address is removed from the Unix Server:

--------------------------------------------------------------------------------------------------------

duval-h#traceroute 10.11.137.21

Type escape sequence to abort.

Tracing the route to mail.benvenue-p.schools.nsw.edu.au (10.11.137.21)

1 itbr12lo1.schools.nsw.edu.au (10.23.250.2) 40 msec 40 msec

itbr21.schools.nsw.edu.au (10.23.254.221) 40 msec

2 itbr21.schools.nsw.edu.au (10.23.254.221) 40 msec 44 msec

benvenue-p.net.det.nsw.edu.au (10.11.254.137) 96 msec

3 benvenue-p.net.det.nsw.edu.au (10.11.254.137) 92 msec 76 msec

mail.benvenue-p.schools.nsw.edu.au (10.11.137.21) 192 msec

[astanislaus]

This is the router which is the default gateway for the Unix Server with 2 x IP Addresses:

---------------------------------------------------------------------------------------------------------

benvenue-p#sho ip int brie

Interface IP-Address OK? Method Status Protocol

BRI0 unassigned YES unset up up

BRI0:1 unassigned YES unset up up

BRI0:2 unassigned YES unset up up

Dialer1 10.11.254.137 YES unset up up

Ethernet0 10.11.137.1 YES NVRAM up up

Loopback0 10.11.254.137 YES NVRAM up up

Virtual-Access1 unassigned YES unset up up

benvenue-p#ping 10.11.137.21

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 10.11.137.21, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms

benvenue-p#ping 10.11.137.28

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 10.11.137.28, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/4 ms

benvenue-p#sho ip arp 10.11.137.21

Protocol Address Age (min) Hardware Addr Type Interface

Internet 10.11.137.21 1 0000.e21f.9eca ARPA Ethernet0

benvenue-p#sho ip arp 10.11.137.30

Protocol Address Age (min) Hardware Addr Type Interface

Internet 10.11.137.30 12 0000.e21f.9eca ARPA Ethernet0

[teru-lei]

HI,

Do you put the two ip address in the same subnet? if so try to put them into different subnets. if you put them in the same subnet, there might be problem.

Best Regards

Teru Lei

[astanislaus]

Same subnet. Cannot put in different subnet.

[teru-lei]

Hi,

Then try to use sub-interface in the router to put the router interface in to different subnet (router on a stack) and then put the NICs to different subnets. It's not recommend to put two NIC in a server to 1 subnet. That may cause problem!

Best Regards

Teru Lei