[ale] Routers, VRRP, and DHCP

[George Allen]

Not sure if this applies to all of GLBP, HSRP, VRRP, but there is a
'redundancy' option to ip helper which lets you make the dhcp-forwarder
aware of the redundancy group:
http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp/command/iap-cr-book/iap-i1.html#wp1413119578
ip helper-address [ vrf name | global ] address { [ redundancy vrg-name ] }

So maybe something like 'ip helper-address 1.2.3.4 redundancy foo'

The docs are a bit sparse on this. Also, I thought I remembered something
about being able to set timing somewhere so one (server or helper) would
respond with some delay after the other, but I can't find it.

There are also ways, to dynamically provision your dhcp pools on the
routers with Embedded Event Manager:
http://www.techexams.net/forums/off-topic/95384-interesting-week-eem-applets-dhcp-ip-sla.html
Using this - you could setup a DHCP on one router, and if that router goes
down the other router bootstraps a pool onto itself with EEM.



On Mon, Sep 14, 2015 at 4:16 PM, Michael Still <stillwaxin at gmail.com> wrote:

>
>
> On Mon, Sep 14, 2015 at 3:30 PM, James Sumners <james.sumners at gmail.com>
> wrote:
>
>>
>> On Mon, Sep 14, 2015 at 3:09 PM, Michael Still <stillwaxin at gmail.com>
>> wrote:
>>
>>> This is fairly standard setup it sounds like. You have a dhcp helper
>>> config on both routers so that if one router is dead the other still passes
>>> along the dhcp requests and updates (note that the log should show it from
>>> the router interface IP and not the vrrp IP). Even though its double talk
>>> this is what you want to see on the dhcp server log to indicate that this
>>> is configured correctly.
>>
>>
>> It does show from the router interface (when I look at a tcpdump of the
>> traffic). How is it that this wouldn't be causing issues with assignment?
>> Shouldn't multiple answers from the same DHCP host confuse the clients?
>>
>
> The client should just use the first response received. Something to keep
> in mind is dhcp state synchronization across your servers if more than one
> server is active on a subnet at any given time.
>
>
>>
>> --
>> James Sumners
>> http://james.sumners.info/ (technical profile)
>> http://jrfom.com/ (personal site)
>> http://haplo.bandcamp.com/ (band page)
>>
>> _______________________________________________
>> Ale mailing list
>> Ale at ale.org
>> http://mail.ale.org/mailman/listinfo/ale
>> See JOBS, ANNOUNCE and SCHOOLS lists at
>> http://mail.ale.org/mailman/listinfo
>>
>>
>
>
> --
> [stillwaxin at gmail.com ~]$ cat .signature
> cat: .signature: No such file or directory
> [stillwaxin at gmail.com ~]$
>
> _______________________________________________
> Ale mailing list
> Ale at ale.org
> http://mail.ale.org/mailman/listinfo/ale
> See JOBS, ANNOUNCE and SCHOOLS lists at
> http://mail.ale.org/mailman/listinfo
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.ale.org/pipermail/ale/attachments/20150914/0152ccae/attachment.html>