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Collisions between PIX 515 and 2601 router

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Aug 29th, 2006
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Hi,


We have a connection between our border router and the gateway firewall through the router's ethernet port and a connection to our ISP host through the router's serial port. The serial interface is fine but the ethernet interface shows a lot of collisions. Both fwall and router ethernet interfaces are set to 10half. On the router change the speed, on the fwall if we change it to 10full the router interface keeps resetting. Any ideas what could cause it and how it can be fixed?

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tinu.karki Tue, 08/29/2006 - 21:29
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Sorry i meant on the router we cant change speed, but on the fwall we can and if we change it to 10 full the router interface keeps resetting so its out of question.

vijayasankar Tue, 08/29/2006 - 22:57
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Hi,


It is quite normal to see collisions on a half duplex link. That's how it works.

If possible, Change the duplex to full at both ends.


On a full duplex link you will never get collisions( unless something is wrong)


-VJ



b.petronio Wed, 08/30/2006 - 02:13
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Best working conditions are equal interface configuration on both sides.

- "if we change it to 10 full the router interface keeps resetting", results of the duplex mismatch , (Full on 1 /Half on the other) .


On the router, when u mean u can't change speed , u have not privileges? or cant find any commands, for changing duplex on that interface.

Try these:

hostname(config)#interface e0/0

hostname(config-if)#half-duplex

hostname(config-if)#full-duplex


If u only could put the Half-Duplex, its impossible not see Colisions.

If u could configure Full-Duplex in both sides and collisions still appear, check out the cabling, and change it if necessary.


Best Regards,

Bruno Petr?nio


spremkumar Wed, 08/30/2006 - 03:04
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Hi


AFAIK Port speed as 10Mbps and duplex as half basically dont go together well at all.


But its the other way around with 10/Half duplex which normally works great.


As the other poster mentioned do check your access level to modify the configuration on the router part.


Also if possible do post out the show verion output taken from your router.


regds


Richard Burts Wed, 08/30/2006 - 05:26
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Edwin


I do not understand your first two sentences:

AFAIK Port speed as 10Mbps and duplex as half basically dont go together well at all.

But its the other way around with 10/Half duplex which normally works great.

which seem to say that 10Mbps half duplex does not go and then says that 10 Mbps half duplex is great. Perhaps you can help me understand what you meant.


It seems to me that the original post is assuming that collisions are bad. That is not necessarily the case. As was pointed out in one of the posts collisions are a fact of life in half duplex Ethernet. Excessive collisions may be a problem - but how do you know whether the number of collisions is excessive? I would suggest to clear the interface counters, let the interface run a bit, then show interface and compare the number of collisions with the total number of output packets.


Another point is that many of the "Ethernet" interfaces (as compared to FastEthernet) are only capable of 10 Mbps and half duplex. This is a restriction of the chip set and does not have anything to do with privilege level or anything like that. Perhaps Tinu can clarify what he meant about not being able to change the interface speed or duplex.


As Bruno pointed out it is important that both sides be configured the same. It is less important whether it is 10 Mbps or 100 Mbps and less important whether it is full duplex or half duplex. A mismatch in either of these parameters is a problem.


HTH


Rick

spremkumar Wed, 08/30/2006 - 05:48
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Hi Rick


I didn't find any supporting document to advocate the chipset limitation which you have clearly mentioned, though i have faced similar kinda issues few years back.Thats the reason i have put in that way.


I have mentioned the same since the original poster was mentioning that the interface is getting reseted when he tries with full duplex.


Also on the second post he has mentioned that he cant change the speed,so thought of probable access issue while configuring the router.



regds


tinu.karki Wed, 08/30/2006 - 16:56
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Rburts is correct , im aware of the commands to change duplex and speed but on the 2601 it wont let change to 100 or full duplex ....i put it down to the router being fairly old (2601), thanks for your help regarding collisions are normal in half duplex, i didnt know this. I was comparing with other connections on the network that had no collisions but have now realised that these are mostly 1gb/100mb full connections.

jackyoung Wed, 08/30/2006 - 18:54
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Your 2601 is not too old that can able to support both half & full duplex. In some old model, e.g. 2501 that require a transiever, where the transiever only support 10 Half, so it always create the problem. Be check the equipment supported mode and matched at both ends. It is fine if one of the port in a switch is 100/Half but other ports are 100/full. The important is the direct connected remote end mode.


Hope this helps.

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