traceroute IP on LAN running HSRP

Answered Question
Nov 24th, 2011
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Hi all,


I have question here .


From my WAN  router when i trace the PC  IP  it shows


2691Router#traceroute 192.168.20.18   PC  IP 

Type escape sequence to abort.
Tracing the route to 192.168.20.18


  1 192.168.6.2 0 msec
    3550SMIA (192.168.5.2) 0 msec
    192.168.6.2 0 msec
  2 192.168.20.18 24 msec 12 msec 16 msec


PC  is connected to switch 3550 A  which is running HSRP  and is active state


192.168.6.2  is IP  of HSRP  standy switch 3550 B.



2691Router#sh cdp nei detail
-------------------------
Device ID: 3550SMIA.manveer.com
Entry address(es):
  IP address: 192.168.5.2
Platform: Cisco WS-C3550-24-PWR,  Capabilities: Router Switch IGMP
Interface: FastEthernet0/1,  Port ID (outgoing port): FastEthernet0/11
Holdtime : 166 sec

Version :
Cisco IOS Software, C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(44)SE6,
RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2009 by Cisco Systems, Inc.
Compiled Mon 09-Mar-09 20:28 by gereddy

advertisement version: 2
Protocol Hello:  OUI=0x00000C, Protocol ID=0x0112; payload len=27, value=0000000
0FFFFFFFF010221FF000000000000000D28BCFD80FF0000
VTP Management Domain: 'manveer.com'
Duplex: full

-------------------------
Device ID: 3550SMIB
Entry address(es):
  IP address: 192.168.6.2
Platform: Cisco WS-C3550-24,  Capabilities: Router Switch IGMP
Interface: FastEthernet1/0,  Port ID (outgoing port): FastEthernet0/11
Holdtime : 142 sec

Version :
Cisco IOS Software, C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(44)SE6,
RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2009 by Cisco Systems, Inc.
Compiled Mon 09-Mar-09 20:28 by gereddy

advertisement version: 2
Protocol Hello:  OUI=0x00000C, Protocol ID=0x0112; payload len=27, value=0000000
0FFFFFFFF010221FF0000000000000009E8A20080FF0000
VTP Management Domain: 'manveer.com'
Duplex: full



My  question is why traceroute shows  192.168.6.2 as first hop 2 times ?

is traffic going via standby switch 3550 B - 192.168.6.2?



Thanks


Mahesh

Correct Answer by Richard Burts about 5 years 8 months ago

Mahesh


What you are seeing is a normal result when you ping from the router and the router has 2 paths to the destination. When it has 2 paths to the destination then the router will do load balancing of the traffic that it sends and it will alternate sending traffic over each of the paths.


So yes some of the traffic is going through the standby switch.


It does not impact traffic from the router whether it goes through the primary switch or the standby switch. It should be equally as fast going through either switch and performance should be just as good on both paths.


When you think about it, the HSRP is running for the hosts connected to subnet 192.168.20.0. The router is not in that subnet and so which switch is primary for subnet 192.168.20.0 makes no diference in how the router sends its traffic.


The HSRP would impact how a host in subnet 192.168.20.0 sends its traffic to the router. But it does not impact how the router sends its traffic to the host.


HTH


Rick

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smitesh kharecha Thu, 11/24/2011 - 20:45
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Hi Mahesh,


Nope, traffic is not going via standby switch.

Generally when in traceroute you see multiple IP address on same hop, it means you have got multiple routes to hop with equal cost/metric/AD.


can you check output of following commands:


show ip route 192.168.20.18

&

show ip route 192.168.6.2


Regards,

Smitesh

mahesh18 Thu, 11/24/2011 - 22:44
User Badges:

Hi,


Thanks for reply.


her e is required info



2691Router#sh ip route 192.168.6.2
Routing entry for 192.168.6.2/31
  Known via "connected", distance 0, metric 0 (connected, via interface)
  Routing Descriptor Blocks:
  * directly connected, via FastEthernet1/0
      Route metric is 0, traffic share count is 1



2691Router#sh ip route 192.168.20.18
Routing entry for 192.168.20.0/24
  Known via "ospf 1", distance 110, metric 2, type intra area
  Last update from 192.168.5.2 on FastEthernet0/1, 09:32:35 ago
  Routing Descriptor Blocks:
  * 192.168.6.2, from 3.3.3.3, 09:32:35 ago, via FastEthernet1/0
      Route metric is 2, traffic share count is 1
    192.168.5.2, from 3.3.3.3, 09:32:35 ago, via FastEthernet0/1
      Route metric is 2, traffic share count is 1


so this is normal behaviour for the network design---?

will it cause any slowdown reaching the LAN  from the router?


2691Router#traceroute 192.168.20.26

Type escape sequence to abort.
Tracing the route to 192.168.20.26

  1 3550SMIA (192.168.5.2) 4 msec
    192.168.6.2 4 msec
    3550SMIA (192.168.5.2) 0 msec
  2 192.168.20.26 4 msec 0 msec 4 msec


so on the traceroute above traffic does not enter standby switch right?

we see switch 3550smia 2 times in hop 1 because from router 2691 it sees two paths for next hops but decides the 3550 switch thats why we see the  3550SMIA (192.168.5.2) 0 msec  right?


thanks

mahesh

smitesh kharecha Thu, 11/24/2011 - 23:14
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Hi Mahesh,


Yes traffic is not going to your standby switch.


You are seeing two entries when you trace to 192.168.20.0 subnet is because you have got two equal cost paths, viz are 192.168.6.2 and 192.168.5.2.


If you compare two traces which you have posted, one for 192.168.20.26 and other for 192.168.20.18; you will notice that traffic is going differently. In case of 192.168.20.26 it is going via 192.168.5.2 and 192.168.20.18 is going via 192.168.6.2.


It is happening becuase of load balancing.


HTH,

Smitesh

mahesh18 Thu, 11/24/2011 - 23:21
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Hi Smitesh,


Now traffic is going via


2691Router#traceroute 192.168.20.18

Type escape sequence to abort.
Tracing the route to 192.168.20.18

  1 3550SMIA (192.168.5.2) 4 msec
    192.168.6.2 0 msec
    3550SMIA (192.168.5.2) 4 msec
  2 192.168.20.18 0 msec 0 msec 0 msec


so now we see it is going via active HSRP  switch earlier it was showing different result do you know why?


thanks


mahesh

smitesh kharecha Fri, 11/25/2011 - 00:37
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  • Silver, 250 points or more

Hi Mahesh,


Seems like I misread your original post.

Also, there is other route (other than your HSRP setup) and therefore it is taking different traces.

Can you please provide me output of following commands on both the 3550 A and B


show standby

show ip route 192.168.20.18

show ip route 192.168.20.26


Regards,

Smitesh

mahesh18 Fri, 11/25/2011 - 08:30
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Hi Smitesh,


Here is  info as per your request


3550 A 


3550SMIA#sh ip route 192.168.20.26
Routing entry for 192.168.20.0/24
  Known via "connected", distance 0, metric 0 (connected, via interface)
  Routing Descriptor Blocks:
  * directly connected, via Vlan20
      Route metric is 0, traffic share count is 1

3550SMIA#sh ip route 192.168.20.18
Routing entry for 192.168.20.0/24
  Known via "connected", distance 0, metric 0 (connected, via interface)
  Routing Descriptor Blocks:
  * directly connected, via Vlan20
      Route metric is 0, traffic share count is 1

3550SMIA#sh stan
3550SMIA#sh standby
Vlan10 - Group 1
  State is Active
    2 state changes, last state change 1w0d
  Virtual IP address is 192.168.10.3
  Active virtual MAC address is 0000.0c07.ac01
    Local virtual MAC address is 0000.0c07.ac01 (v1 default)
  Hello time 3 sec, hold time 10 sec
    Next hello sent in 0.220 secs
  Authentication text "manveer"
  Preemption enabled, delay min 120 secs
  Active router is local
  Standby router is 192.168.10.2, priority 100 (expires in 8.564 sec)
  Priority 150 (configured 150)
  IP redundancy name is "hsrp-Vl10-1" (default)
Vlan20 - Group 0
  State is Active
    2 state changes, last state change 1w0d
  Virtual IP address is 192.168.20.3
  Active virtual MAC address is 0000.0c07.ac00
    Local virtual MAC address is 0000.0c07.ac00 (v1 default)
  Hello time 3 sec, hold time 10 sec
    Next hello sent in 0.220 secs
  Preemption enabled
  Active router is local
  Standby router is 192.168.20.2, priority 100 (expires in 9.892 sec)
  Priority 150 (configured 150)
  IP redundancy name is "hsrp-Vl20-0" (default)



*****************************



3550SMIB#sh standby
Vlan10 - Group 1
  State is Standby
    7 state changes, last state change 1w0d
  Virtual IP address is 192.168.10.3
  Active virtual MAC address is 0000.0c07.ac01
    Local virtual MAC address is 0000.0c07.ac01 (v1 default)
  Hello time 3 sec, hold time 10 sec
    Next hello sent in 0.564 secs
  Authentication text "manveer"
  Preemption enabled, delay min 60 secs
  Active router is 192.168.10.1, priority 150 (expires in 9.224 sec)
  Standby router is local
  Priority 100 (default 100)
  IP redundancy name is "hsrp-Vl10-1" (default)
Vlan20 - Group 0
  State is Standby
    4 state changes, last state change 1w0d
  Virtual IP address is 192.168.20.3
  Active virtual MAC address is 0000.0c07.ac00
    Local virtual MAC address is 0000.0c07.ac00 (v1 default)
  Hello time 3 sec, hold time 10 sec
    Next hello sent in 1.888 secs
  Preemption enabled
  Active router is 192.168.20.1, priority 150 (expires in 9.220 sec)
  Standby router is local
  Priority 100 (default 100)
  IP redundancy name is "hsrp-Vl20-0" (default)
3550SMIB#sh ip route 192.168.20.26
Routing entry for 192.168.20.0/24
  Known via "connected", distance 0, metric 0 (connected, via interface)
  Routing Descriptor Blocks:
  * directly connected, via Vlan20
      Route metric is 0, traffic share count is 1

3550SMIB#sh ip route 192.168.20.18
Routing entry for 192.168.20.0/24
  Known via "connected", distance 0, metric 0 (connected, via interface)
  Routing Descriptor Blocks:
  * directly connected, via Vlan20
      Route metric is 0, traffic share count is 1



Thanks


mahesh

Correct Answer
Richard Burts Fri, 11/25/2011 - 11:30
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Mahesh


What you are seeing is a normal result when you ping from the router and the router has 2 paths to the destination. When it has 2 paths to the destination then the router will do load balancing of the traffic that it sends and it will alternate sending traffic over each of the paths.


So yes some of the traffic is going through the standby switch.


It does not impact traffic from the router whether it goes through the primary switch or the standby switch. It should be equally as fast going through either switch and performance should be just as good on both paths.


When you think about it, the HSRP is running for the hosts connected to subnet 192.168.20.0. The router is not in that subnet and so which switch is primary for subnet 192.168.20.0 makes no diference in how the router sends its traffic.


The HSRP would impact how a host in subnet 192.168.20.0 sends its traffic to the router. But it does not impact how the router sends its traffic to the host.


HTH


Rick

mahesh18 Fri, 11/25/2011 - 13:16
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Hi Rick,


Many thanks once again for clearing my concepts  on traceroute HSRP.

Its always good to read your answers.


Regards

Mahesh

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