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Bronze

Traceroute and multiple links

I have 6 links to a neighbor router.

All links are equal cost, operational and passing traffic.

When I traceroute to the next hop loopback address, traceroute ONLY uses 3 of the six paths.

ANYONE know why?

OER-Master1#sh ip eigrp top

IP-EIGRP Topology Table for AS(90)/ID(172.26.3.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,

r - reply Status, s - sia Status

P 172.26.0.14/32, 1 successors, FD is 128256

via Connected, Loopback0

P 172.26.0.15/32, 4 successors, FD is 130816

via 172.26.2.2 (130816/128256), GigabitEthernet0/0.2

via 172.26.4.2 (130816/128256), GigabitEthernet0/0.4

via 172.26.5.2 (130816/128256), GigabitEthernet0/0.5

via 172.26.6.2 (130816/128256), GigabitEthernet0/0.6

via 172.26.1.2 (130816/128256), GigabitEthernet0/0.1

via 172.26.7.2 (130816/128256), GigabitEthernet0/0.7

OER-Master1#traceroute 172.26.0.15

Type escape sequence to abort.

Tracing the route to 172.26.0.15

1 172.26.6.2 0 msec

172.26.5.2 4 msec

172.26.4.2 0 msec

OER-Master1#

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Silver

Re: Traceroute and multiple links

Hello Franck,

4 paths is the default for EIGRP

have you added

router eigpr ASN

maximum-paths 6

otherwise only 4 successors are installed in the routing table

in other words

until you don't see all 6 paths in the ip routing table with sh ip route you cannot be sure they are all used.

Hope to help

Giuseppe

4 REPLIES
Hall of Fame Super Silver

Re: Traceroute and multiple links

Hello Franck,

traceroute defaults to use three probes for each TTL so it cannot discover 6 paths.

you need to use extended traceroute and to modify the number of probes sent to a number >= 6 to see this.

that is

traceroute

Hope to help

Giuseppe

Bronze

Re: Traceroute and multiple links

Hi Giuseppe,

I did not know this fact.

Excellent THANKS.

I could only get the Cisco IOS to use 4 links. Since this is new IOS in a lab environment and not critical -YET, I will accept the results for now.

BTW, I specified 6, 12, 24 and 100 probes and received the same results.

IOS on Cisco 3845 router.

flash:c3845-advipservicesk9-mz.124-11.XJ4.bin"

OER-Master1#traceroute

Protocol [ip]:

Target IP address: 172.26.0.15

Source address: 172.26.0.14

Numeric display [n]:

Timeout in seconds [3]:

Probe count [3]: 100

Minimum Time to Live [1]:

Maximum Time to Live [30]:

Port Number [33434]:

Loose, Strict, Record, Timestamp, Verbose[none]:

Type escape sequence to abort.

Tracing the route to 172.26.0.15

1 172.26.4.2 4 msec

172.26.2.2 0 msec

172.26.6.2 0 msec

172.26.5.2 4 msec *

172.26.2.2 0 msec

172.26.6.2 0 msec

172.26.5.2 4 msec

172.26.4.2 0 msec *

172.26.6.2 0 msec

172.26.5.2 0 msec

172.26.4.2 4 msec

172.26.2.2 0 msec *

172.26.5.2 0 msec

172.26.4.2 0 msec

172.26.2.2 4 msec

172.26.6.2 0 msec *

172.26.4.2 0 msec

172.26.2.2 0 msec

172.26.6.2 4 msec

172.26.5.2 0 msec *

172.26.2.2 0 msec

172.26.6.2 0 msec

172.26.5.2 4 msec

172.26.4.2 0 msec *

172.26.6.2 0 msec

172.26.5.2 0 msec

172.26.4.2 4 msec

172.26.2.2 0 msec *

172.26.5.2 0 msec

172.26.4.2 0 msec

172.26.2.2 4 msec

172.26.6.2 0 msec *

172.26.4.2 0 msec

172.26.2.2 0 msec

172.26.6.2 4 msec

172.26.5.2 0 msec *

172.26.2.2 0 msec

172.26.6.2 0 msec

172.26.5.2 4 msec

172.26.4.2 0 msec *

172.26.6.2 0 msec

172.26.5.2 0 msec

172.26.4.2 4 msec

172.26.2.2 0 msec *

172.26.5.2 0 msec

172.26.4.2 0 msec

172.26.2.2 4 msec

172.26.6.2 0 msec

--snip--

ctrl-shift 6

These are the interfaces on the next hop router where 172.26.0.15 resides.

OER-Master1#ping 172.26.1.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.26.1.2, timeout is 2 seconds:

!!!!!

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

OER-Master1#ping 172.26.2.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.26.2.2, timeout is 2 seconds:

!!!!!

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

OER-Master1#ping 172.26.4.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.26.4.2, timeout is 2 seconds:

!!!!!

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

OER-Master1#ping 172.26.5.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.26.5.2, timeout is 2 seconds:

!!!!!

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

OER-Master1#ping 172.26.6.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.26.6.2, timeout is 2 seconds:

!!!!!

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

OER-Master1#ping 172.26.7.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.26.7.2, timeout is 2 seconds:

!!!!!

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

OER-Master1#

Hall of Fame Super Silver

Re: Traceroute and multiple links

Hello Franck,

4 paths is the default for EIGRP

have you added

router eigpr ASN

maximum-paths 6

otherwise only 4 successors are installed in the routing table

in other words

until you don't see all 6 paths in the ip routing table with sh ip route you cannot be sure they are all used.

Hope to help

Giuseppe

Bronze

Re: Traceroute and multiple links

THANKS,

I thought the EIGRP default was 6. :(

OER-Master1(config)#router eigrp 90

OER-Master1(config-router)#maximum-paths 16

OER-Master1(config-router)#end

OER-Master1#

OER-Master1#traceroute

Protocol [ip]:

Target IP address: 172.26.0.15

Source address: 172.26.0.14

Numeric display [n]:

Timeout in seconds [3]:

Probe count [3]: 6

Minimum Time to Live [1]:

Maximum Time to Live [30]:

Port Number [33434]:

Loose, Strict, Record, Timestamp, Verbose[none]:

Type escape sequence to abort.

Tracing the route to 172.26.0.15

1 172.26.7.2 0 msec

172.26.6.2 4 msec

172.26.5.2 0 msec

172.26.4.2 0 msec

172.26.2.2 4 msec

172.26.1.2 0 msec

OER-Master1#

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