Mailing List Archive: nsp: juniper

proxy arp C vs J

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biwa2go at gmail

Feb 6, 2012, 11:56 AM

Post #1 of 8 (1065 views)
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proxy arp C vs J

Hi Guys
We are experiencing some issues in one of our client sites,

Basically we migrate from a Cisco to a Juniper MX80, and since there has
been some issues, mainly we are seeing IP addresses being shared by 2-3
mac address, to be precise , mac address being rewritten , ie: one IP is
being seen on the Juniper owned by 3 different mac address within one hour
( the 1st mac address is being re-writen by the 2nd one and then 2nd by
the 3rd mac).

This is causing a lot of users not having any kind of internet
connectivity.When we rollback to the Cisco device , this issue does not
occur.

After investigation we can safely eliminates the DHCP server being the
cause of issue (, also proved when Cisco is roll back in the topology),

The config of the Cisco is fairly simple and is almost 99.99% than the one
being copied over to the Juniper.

One thing we notice is that both Cisco and Juniper has proxy-arp configured
on some of the interface, and we are planning in our next maintenance to
disable it.

my question is: is the proxy-arp behavior in Juniper slightly different
than the Cisco ?

thanks for your inputs
_______________________________________________
juniper-nsp mailing list juniper-nsp [at] puck
https://puck.nether.net/mailman/listinfo/juniper-nsp

biwa2go at gmail

Feb 6, 2012, 11:57 AM

Post #2 of 8 (1024 views)
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Re: proxy arp C vs J [In reply to]

Forgot to add we are running MX80 on Junos 11.2

On 6 February 2012 19:56, biwa net <biwa2go [at] gmail> wrote:

> Hi Guys
> We are experiencing some issues in one of our client sites,
>
> Basically we migrate from a Cisco to a Juniper MX80, and since there has
> been some issues, mainly we are seeing IP addresses being shared by 2-3
> mac address, to be precise , mac address being rewritten , ie: one IP is
> being seen on the Juniper owned by 3 different mac address within one hour
> ( the 1st mac address is being re-writen by the 2nd one and then 2nd by
> the 3rd mac).
>
> This is causing a lot of users not having any kind of internet
> connectivity.When we rollback to the Cisco device , this issue does not
> occur.
>
> After investigation we can safely eliminates the DHCP server being the
> cause of issue (, also proved when Cisco is roll back in the topology),
>
> The config of the Cisco is fairly simple and is almost 99.99% than the one
> being copied over to the Juniper.
>
> One thing we notice is that both Cisco and Juniper has proxy-arp
> configured on some of the interface, and we are planning in our next
> maintenance to disable it.
>
> my question is: is the proxy-arp behavior in Juniper slightly different
> than the Cisco ?
>
> thanks for your inputs
>
_______________________________________________
juniper-nsp mailing list juniper-nsp [at] puck
https://puck.nether.net/mailman/listinfo/juniper-nsp

per.granath at gcc

Feb 6, 2012, 11:20 PM

Post #3 of 8 (1022 views)
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Re: proxy arp C vs J [In reply to]

Try the command:
no-gratuitous-arp-request

> > Basically we migrate from a Cisco to a Juniper MX80, and since there
> > has been some issues, mainly we are seeing IP addresses being shared
> > by 2-3 mac address, to be precise , mac address being rewritten , ie:
> > one IP is being seen on the Juniper owned by 3 different mac address
> > within one hour ( the 1st mac address is being re-writen by the 2nd
> > one and then 2nd by the 3rd mac).

_______________________________________________
juniper-nsp mailing list juniper-nsp [at] puck
https://puck.nether.net/mailman/listinfo/juniper-nsp

mtinka at globaltransit

Feb 7, 2012, 2:18 AM

Post #4 of 8 (1026 views)
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Re: proxy arp C vs J [In reply to]

On Tuesday, February 07, 2012 03:57:55 AM biwa net wrote:

> Forgot to add we are running MX80 on Junos 11.2

Can you send a sample topology and your interface
configurations for the Cisco and Juniper routers?

Mark.

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alex.arseniev at gmail

Feb 7, 2012, 2:23 AM

Post #5 of 8 (1012 views)
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Re: proxy arp C vs J [In reply to]

Did you check what MACs are used in 1st, 2nd and 3rd time? Specifically MAC
OUIs.
I suspect this is a side effect of having C-J in the same broadcast domain.
Basically, when J-interface ARPs for a connected host, _AND_ if C has a
specific route to that host/32, the C will answer with own MAC.
I have seen this myself many times and I suggest to disable proxy-arp on C
to get rid of this behavior.
HTH
Thanks
Alex

----- Original Message -----
From: "biwa net" <biwa2go [at] gmail>
To: <juniper-nsp [at] puck>
Sent: Monday, February 06, 2012 7:57 PM
Subject: Re: [j-nsp] proxy arp C vs J

> Forgot to add we are running MX80 on Junos 11.2
>
> On 6 February 2012 19:56, biwa net <biwa2go [at] gmail> wrote:
>
>> Hi Guys
>> We are experiencing some issues in one of our client sites,
>>
>> Basically we migrate from a Cisco to a Juniper MX80, and since there has
>> been some issues, mainly we are seeing IP addresses being shared by 2-3
>> mac address, to be precise , mac address being rewritten , ie: one IP is
>> being seen on the Juniper owned by 3 different mac address within one
>> hour
>> ( the 1st mac address is being re-writen by the 2nd one and then 2nd by
>> the 3rd mac).
>>
>> This is causing a lot of users not having any kind of internet
>> connectivity.When we rollback to the Cisco device , this issue does not
>> occur.
>>
>> After investigation we can safely eliminates the DHCP server being the
>> cause of issue (, also proved when Cisco is roll back in the topology),
>>
>> The config of the Cisco is fairly simple and is almost 99.99% than the
>> one
>> being copied over to the Juniper.
>>
>> One thing we notice is that both Cisco and Juniper has proxy-arp
>> configured on some of the interface, and we are planning in our next
>> maintenance to disable it.
>>
>> my question is: is the proxy-arp behavior in Juniper slightly different
>> than the Cisco ?
>>
>> thanks for your inputs
>>
> _______________________________________________
> juniper-nsp mailing list juniper-nsp [at] puck
> https://puck.nether.net/mailman/listinfo/juniper-nsp
>

_______________________________________________
juniper-nsp mailing list juniper-nsp [at] puck
https://puck.nether.net/mailman/listinfo/juniper-nsp

jof at thejof

Feb 7, 2012, 2:38 AM

Post #6 of 8 (1022 views)
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Re: proxy arp C vs J [In reply to]

On Tue, Feb 7, 2012 at 2:23 AM, Alex Arseniev <alex.arseniev [at] gmail> wrote:
> Did you check what MACs are used in 1st, 2nd and 3rd time? Specifically MAC
> OUIs.
> I suspect this is a side effect of having C-J in the same broadcast domain.
> Basically, when J-interface ARPs for a connected host, _AND_ if C has a
> specific route to that host/32, the C will answer with own MAC.

And potentially, depending on the configuration, the Cisco may try and
proxy based on a route learned from the Juniper, creating a loop.

The question I would ask: what is proxy arp used for? why?

Cheers,
jof
_______________________________________________
juniper-nsp mailing list juniper-nsp [at] puck
https://puck.nether.net/mailman/listinfo/juniper-nsp

gordon at gswsystems

Feb 7, 2012, 4:10 PM

Post #7 of 8 (1009 views)
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Re: proxy arp C vs J [In reply to]

Proxy ARP can be useful while sorting out a broken (misconfigured) network,
but can also cause you a lot of grief.
If the network is configured correctly, it's just a hindrance. Most
definitely turn it off, then fix any routing issues it was masking.

I see someone mentioned turning off gratuitous arps, but I'd only do that if
really necessary, as its very useful for forcing a refresh of an entry e.g.
E-Series cable customers

Cheers,
Gordon

-----Original Message-----
From: juniper-nsp-bounces [at] puck
[mailto:juniper-nsp-bounces [at] puck] On Behalf Of biwa net
Sent: Tuesday, 7 February 2012 5:57 a.m.
To: juniper-nsp [at] puck
Subject: [j-nsp] proxy arp C vs J

Hi Guys
We are experiencing some issues in one of our client sites,

Basically we migrate from a Cisco to a Juniper MX80, and since there has
been some issues, mainly we are seeing IP addresses being shared by 2-3 mac
address, to be precise , mac address being rewritten , ie: one IP is being
seen on the Juniper owned by 3 different mac address within one hour ( the
1st mac address is being re-writen by the 2nd one and then 2nd by the 3rd
mac).

This is causing a lot of users not having any kind of internet
connectivity.When we rollback to the Cisco device , this issue does not
occur.

After investigation we can safely eliminates the DHCP server being the cause
of issue (, also proved when Cisco is roll back in the topology),

The config of the Cisco is fairly simple and is almost 99.99% than the one
being copied over to the Juniper.

One thing we notice is that both Cisco and Juniper has proxy-arp configured
on some of the interface, and we are planning in our next maintenance to
disable it.

my question is: is the proxy-arp behavior in Juniper slightly different than
the Cisco ?

thanks for your inputs
_______________________________________________
juniper-nsp mailing list juniper-nsp [at] puck
https://puck.nether.net/mailman/listinfo/juniper-nsp

_______________________________________________
juniper-nsp mailing list juniper-nsp [at] puck
https://puck.nether.net/mailman/listinfo/juniper-nsp

mtinka at globaltransit

Feb 20, 2012, 8:33 PM

Post #8 of 8 (936 views)
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Re: proxy arp C vs J [In reply to]

On Wednesday, February 08, 2012 08:10:59 AM Gordon Smith
wrote:

> Proxy ARP can be useful while sorting out a broken
> (misconfigured) network, but can also cause you a lot of
> grief.
> If the network is configured correctly, it's just a
> hindrance. Most definitely turn it off, then fix any
> routing issues it was masking.

That and ICMP Redirects.

Mark.

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