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Explaination on traceroute

‎05-24-2016 08:31 PM

I am running protocol ospf on my lab Router.I have a load balancing policy configured on the forwarding table on my Router. The detialed output for an external route seen in the routing table is as below.

 

admin@R6# run show route 172.30.63.1/32 detail 

inet.0: 56 destinations, 64 routes (56 active, 0 holddown, 0 hidden)
172.30.63.1/32 (1 entry, 1 announced)
        *OSPF   Preference: 150
                Next hop type: Router, Next hop index: 262149
                Address: 0x94e4280
                Next-hop reference count: 73
                Next hop: 172.16.0.29 via ge-0/0/4.123
                Next hop: 172.16.0.37 via ge-0/0/4.135, selected
                State: <Active Int Ext>
                Local AS: 4012345678 
                Age: 6:41       Metric: 1       Tag: 2624 
                Task: OSPF
                Announcement bits (3): 0-KRT 4-LDP 7-Resolve tree 2 
                AS path: I

inet.3: 35 destinations, 42 routes (6 active, 0 holddown, 34 hidden)

The forwarding table is also showing 2 next hops installed in it for this external route.

 

admin@R6# run show route forwarding-table destination 172.30.63.1 
Routing table: default.inet
Internet:
Destination        Type RtRef Next hop           Type Index NhRef Netif
172.30.63.1/32     user     0                    ulst 262149    24
                              172.16.0.29        ucst   625     5 ge-0/0/4.123
                              172.16.0.37        ucst   626    13 ge-0/0/4.135

Routing table: __master.anon__.inet
Internet:
Destination        Type RtRef Next hop           Type Index NhRef Netif
default            perm     0                    rjct   527     1

The Trace for this external route is as below.

admin@R6# run traceroute 172.30.63.1 no-resolve    
traceroute to 172.30.63.1 (172.30.63.1), 30 hops max, 40 byte packets
 1  172.16.0.29  14.933 ms  14.972 ms 172.16.0.37  19.948 ms
 2  172.16.0.21  19.811 ms 172.16.0.13  19.937 ms  20.364 ms
 3  172.30.63.1  24.715 ms  24.814 ms 172.16.0.10  25.117 ms

[edit]
admin@R6# run traceroute 172.30.63.1 no-resolve    
traceroute to 172.30.63.1 (172.30.63.1), 30 hops max, 40 byte packets
 1  172.16.0.37  14.973 ms 172.16.0.29  14.855 ms  14.969 ms
 2  172.16.0.21  20.138 ms  20.070 ms 172.16.0.13  19.780 ms
 3  172.16.0.10  25.012 ms 172.30.63.1  24.665 ms  25.152 ms

I am confused in the output of traceroute that why it is showing two next-hops in every line of trace for this route. In line 1 it is showing 172.16.0.37 as well as 172.16.0.29. Is it because of load-balancing configured on my router?? Can anyone explain in detail ?? The topology diagram is also attached.

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5 REPLIES 5
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Re: Explaination on traceroute

‎05-24-2016 09:40 PM

Hi,

Greeting !!!

 

I suppose, it is because of LB policy which you configure. Hence one paket he send on "172.16.0.29"  next-hop address and second packet send on "172.16.0.37".

 

Cheers Smiley Happy

Vinay

Regards,
Vinay
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Re: Explaination on traceroute

‎05-25-2016 12:00 PM

If you may please explain in detail.

 

Any links to explain this.

 

regards

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Re: Explaination on traceroute

‎05-25-2016 10:28 PM

I think you have configured something like this

Routing

Re: Explaination on traceroute

‎05-25-2016 10:56 PM

One more ... you can compare traceroute from RE and traceroute from host behind this router. trace will be different. 

 

From RE on your first hp yoou will always see all nexthops , from host behind router on the second hop you will see only one nexthop every time.  This is RE originating traffic always balanced per-packet(real per packet , not per flow) 

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Re: Explaination on traceroute

‎05-31-2016 07:27 PM


http://www.juniper.net/documentation/en_US/junos13.3/topics/concept/policy-per-packet-load-balancing...
http://www.juniper.net/techpubs/en_US/junos12.3/topics/concept/policy-per-packet-load-balancing-over...
http://www.juniper.net/techpubs/en_US/junos12.3/topics/usage-guidelines/policy-configuring-per-packe...

 

These articles should help explain in details. Not sure we are understanding what you do not understand about load balancing. You have configured it and it is working as designed.

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