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IP Helper Redundancy - HSRP

Noble
Level 1
Level 1

Hello,

 

I have two ASR 1001X routers configured with HSRP and IP helper addresses on the interfaces for DHCP address assignment.  I'm currently having an issue that's been observed when two routers in HSRP, configured with helper-address forward the request to the DHCP server simultaneously.  The solution is to have only the primary device forward the request and it's recommended that you apply the "IP Helper-address X.X.X.X redundancy" command to alleviate this issue, however this command is not available to me, and I believe it's been deprecated.

 

Is there an alternative command or configuration I can implement to achieve the desired affect?  There are recommendations from Microsoft to delay the forwarding from the relay agent, however this doesn't seem possible either.  I've also tried delaying the address distribution on the DHCP server itself but haven't had much luck.

 

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp/configuration/15-mt/iap-15-mt-book/iap-udp-vrg.html

 

https://learningnetwork.cisco.com/docs/DOC-25784

 

Thanks.

1 Accepted Solution

Accepted Solutions

Alex Pfeil
Level 7
Level 7

This is not a best practice, but may meet your requirement.

Create an IP SLA on the standby router monitoring the active router.

Create an EEM script on the standby router which places the ip helper-address command on the necessary interfaces, when sla is down, and removes them, when it is up.

I have not tested this but I believe it will work.

You can work with the SLA timers to get it to where you need it to be.

 

Please rate helpful posts.

View solution in original post

2 Replies 2

Alex Pfeil
Level 7
Level 7

This is not a best practice, but may meet your requirement.

Create an IP SLA on the standby router monitoring the active router.

Create an EEM script on the standby router which places the ip helper-address command on the necessary interfaces, when sla is down, and removes them, when it is up.

I have not tested this but I believe it will work.

You can work with the SLA timers to get it to where you need it to be.

 

Please rate helpful posts.

Thank you - this was the solution/workaround that TAC provided as well.

 

Just for reference, the commands would look something like below (applied on the STANDBY device only):

 

event manager applet HSRP-8-Up authorization bypass
event syslog pattern "Grp 8 state Standby -> Active"
action 1.1 cli command "en"
action 1.2 cli command "conf t"
action 1.3 cli command "int gi0/0/0.8"
action 1.4 cli command "ip helper-address X.X.X.X"
action 1.5 cli command "ip helper-address X.X.X.X"


event manager applet HSRP-8-Down authorization bypass
event syslog pattern "Grp 8 state Speak -> Standby"
action 1.1 cli command "en"
action 1.2 cli command "conf t"
action 1.3 cli command "int gi0/0/0.8"
action 1.4 cli command "no ip helper-address X.X.X.X"
action 1.5 cli command "no ip helper-address X.X.X.X"

 

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