Re: [MT-AU Public] Public Digest, Vol 2, Issue 3
Mike, I've experienced a very similar issue, but slightly different. In the transition from version 5 to version 6 they made some change to the DHCP server that prevents it from working with Cisco 3550/3560 switches running stock DHCP snooping. The switches grab the packets, add option 82 and pass it on. When the Mikrotik DHCP server responds with an offer packet it doesn't send subnet/default gateway/dns. If you tell the switches to NOT use option 82, everything magically starts working. I did a writeup about it here(http://gregsowell.com/?p=4773)...even include some packet captures showing the wackyness. Good luck guys! Greg On Wed, Apr 2, 2014 at 8:00 PM, <public-request@talk.mikrotik.com.au> wrote:
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Today's Topics:
1. DHCP bug rOSv6.10 (at least) (Mike Everest)
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Message: 1 Date: Wed, 2 Apr 2014 14:58:25 +1100 From: "Mike Everest" <mike@duxtel.com> To: <public@talk.mikrotik.com.au> Subject: [MT-AU Public] DHCP bug rOSv6.10 (at least) Message-ID: <08fe01cf4e27$cca54cf0$65efe6d0$@duxtel.com> Content-Type: text/plain; charset="us-ascii"
Hi Folks,
I have received report of this bug behaviour before, but never seen it happen myself, or been able to get any diagnostic at all until this afternoon. Thought I would post in case it is useful info!
This has been reported to us previously as "when customer gets DHCP lease, no access to anything is possible. When customer enters static lease, everything is good. Reboot router, everything fine again for a while. Then stops working"
Today, I discovered the reason. After some number of leases has been issued by DHCP server, some number in the vicinity of about 200 leases, new leases are issued with bad subnet mask, no gateway and no DNS. End result, of course, is no connectivity.
This is apparently just related to number of leases, not actual dhcp server - i.e. the problem happens after the same number of leases are formed even when there are 3 DHCP servers on 4 different subnetworks, or just one DHCP server for all clients.
Today, I had a chance to work with a fellow who had done some much better diagnostic work on a network experiencing essentially the same behaviour - he discovered that DHCP becomes broken after some time (or some number of leases) in that clients no longer receive netmask, gateway or DNS detail. Thus the client picks up IP address only, and a default mask (assume based on address 'class') and blank gateway and DNS.
The routerOS version in place omn that network is 6.10 - we have upgraded to 6.11 and see if it happens again.
If so, we'll grab some pcaps of DHCP traffic and report to MT - in the meantime, if anyone has experience with this issue too, please post it! ;)
Cheers, Mike.
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Subject: Digest Footer
_______________________________________________ Public mailing list Public@talk.mikrotik.com.au http://talk.mikrotik.com.au/mailman/listinfo/public_talk.mikrotik.com.au
------------------------------
End of Public Digest, Vol 2, Issue 3 ************************************
-- GregSowell.com TheBrothersWISP.com
-----Original Message----- From: Public [mailto:public-bounces@talk.mikrotik.com.au] On Behalf Of Greg Sowell Sent: Thursday, 3 April 2014 1:51 PM To: public@talk.mikrotik.com.au Subject: Re: [MT-AU Public] Public Digest, Vol 2, Issue 3
Mike,
I've experienced a very similar issue, but slightly different. In the
Nice, nice, nice! Thanks Greg! Damn brilliant :-D That said, we have not seen recurrence (yet!) since update to v6.11 - surely they didn't do something about it? (there's nothing about it in the release notes! ;-) Cheers, Mike. transition
from version 5 to version 6 they made some change to the DHCP server that prevents it from working with Cisco 3550/3560 switches running stock DHCP snooping. The switches grab the packets, add option 82 and pass it on. When the Mikrotik DHCP server responds with an offer packet it doesn't send subnet/default gateway/dns. If you tell the switches to NOT use option 82, everything magically starts working. I did a writeup about it here(http://gregsowell.com/?p=4773)...even include some packet captures showing the wackyness.
Good luck guys!
Greg
On Wed, Apr 2, 2014 at 8:00 PM, <public-request@talk.mikrotik.com.au> wrote:
Send Public mailing list submissions to public@talk.mikrotik.com.au
To subscribe or unsubscribe via the World Wide Web, visit
http://talk.mikrotik.com.au/mailman/listinfo/public_talk.mikrotik.com. au
or, via email, send a message with subject or body 'help' to public-request@talk.mikrotik.com.au
You can reach the person managing the list at public-owner@talk.mikrotik.com.au
When replying, please edit your Subject line so it is more specific than "Re: Contents of Public digest..."
Today's Topics:
1. DHCP bug rOSv6.10 (at least) (Mike Everest)
----------------------------------------------------------------------
Message: 1 Date: Wed, 2 Apr 2014 14:58:25 +1100 From: "Mike Everest" <mike@duxtel.com> To: <public@talk.mikrotik.com.au> Subject: [MT-AU Public] DHCP bug rOSv6.10 (at least) Message-ID: <08fe01cf4e27$cca54cf0$65efe6d0$@duxtel.com> Content-Type: text/plain; charset="us-ascii"
Hi Folks,
I have received report of this bug behaviour before, but never seen it happen myself, or been able to get any diagnostic at all until this afternoon. Thought I would post in case it is useful info!
This has been reported to us previously as "when customer gets DHCP lease, no access to anything is possible. When customer enters static lease, everything is good. Reboot router, everything fine again for a while. Then stops working"
Today, I discovered the reason. After some number of leases has been issued by DHCP server, some number in the vicinity of about 200 leases, new leases are issued with bad subnet mask, no gateway and no DNS. End result, of course, is no connectivity.
This is apparently just related to number of leases, not actual dhcp server - i.e. the problem happens after the same number of leases are formed even when there are 3 DHCP servers on 4 different subnetworks, or just one DHCP server for all clients.
Today, I had a chance to work with a fellow who had done some much better diagnostic work on a network experiencing essentially the same behaviour - he discovered that DHCP becomes broken after some time (or some number of leases) in that clients no longer receive netmask, gateway or DNS detail. Thus the client picks up IP address only, and a default mask (assume based on address 'class') and blank gateway and DNS.
The routerOS version in place omn that network is 6.10 - we have upgraded to 6.11 and see if it happens again.
If so, we'll grab some pcaps of DHCP traffic and report to MT - in the meantime, if anyone has experience with this issue too, please post it! ;)
Cheers, Mike.
------------------------------
Subject: Digest Footer
_______________________________________________ Public mailing list Public@talk.mikrotik.com.au http://talk.mikrotik.com.au/mailman/listinfo/public_talk.mikrotik.com. au
------------------------------
End of Public Digest, Vol 2, Issue 3 ************************************
--
GregSowell.com TheBrothersWISP.com _______________________________________________ Public mailing list Public@talk.mikrotik.com.au http://talk.mikrotik.com.au/mailman/listinfo/public_talk.mikrotik.com.au
participants (2)
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Greg Sowell -
Mike Everest