RE: OSPF cost - LAN segment

Pavel,

That's most likely an NM-4T on your 3725, right? Those ports always default to 128kbps for software bandwidth.

-ryan

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Pavel Bykov
Sent: Thursday, May 21, 2009 8:34 AM
To: Paul Cosgrove
Cc: Welly Kamarudin; ccielab_at_groupstudy.com
Subject: Re: OSPF cost - LAN segment

Thanks for the correction Paul.
Before I posted that I tried it out on a 3725, but it turns out it was a
coincidence. I set the clock rate to 128000, and this was the output:

interface Serial1/1
 description >> RackYY-R1 S0/1 <<
 ip address 1.1.1.1 255.255.255.0
 encapsulation ppp
 clock rate 128000
 no dce-terminal-timing-enable
end

BB1-3725#sh int s 1/1 | in BW
  MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,

Because if I set clock rate to anything, BW will still be 128000:

interface Serial1/1
 description >> RackYY-R1 S0/1 <<
 ip address 1.1.1.1 255.255.255.0
 encapsulation ppp
 clock rate 64000
 no dce-terminal-timing-enable
end

BB1-3725#sh int s 1/1 | in BW
  MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,

What led me to believe that the BW will change, is that I thought there
should be 1544 if there is no influence of BW by clock rate.
But it just turned out to be a controller, that can have highest speed of
128000:
BB1-3725#sh controllers s 1/1
CD2430 Slot 1, Port 1, Controller 0, Channel 1, Revision 19
Channel mode is synchronous serial

So yeah, sorry for the misinformation.

On Thu, May 21, 2009 at 12:57 PM, Paul Cosgrove <paul.cosgrove_at_gmail.com>wrote:

> Pavel Bykov wrote:
>
> If it is all default config, there probably will be a different cost,
>> because when you use clock rate on DCE interface, bandwidth will be set to
>> the clock rate and cost will be huge. But on DTE interface, it will still
>> be
>> 1536kbps. so you'd need to synchronize bandwidth parameters there
>>
>>
>
> The 'clock rate' command has no effect on the 'bandwidth' command, whether
> the interface is DCE or DTE. Unless you also set bandwidth manually, for a
> T1 interface the bandwidth will be 1544, and so OSPF uses a cost of 64. You
> could configure bandwidth to be much higher than the clock rate, if you
> really want to.
> It is of course important that you configure appropriate values using the
> bandwidth command, for various routing and QoS considerations but also to
> make it easier for others to understand the network. This does not
> necessarily mean that bandwidth values should match between neighboring
> routers, a common example where the values often differ occurring with hub
> and spoke frame relay.
> Paul.
>
>
>
>>
>>
>
>

-- 
Pavel Bykov
----------------
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