From: Peng Zheng (zpnist@xxxxxxxxx)
Date: Thu Aug 29 2002 - 01:21:17 GMT-3
But I don't think so.
Because when bgp always-compare-med enabled:
AS(PATH) 500, med 100, internal, rid 172.16.8.4
always is chosen as the best path although the entry
change from 3 to 2.
That's what I said.
--- "Volkov, Dmitry (Toronto - BCE)"
<dmitry_volkov@ca.ml.com> wrote:
> Peng,
>
> You are NOT right. Read it
> http://www.cisco.com/warp/customer/459/bgp-med.html
> carefully:
>
> Example 2: bgp deterministic-med Disabled, bgp
> always-compare-med Enabled
> ENTRY1 IS COMPARED TO ENTRY2. These entries are from
> DIFFERENT neighbor ASs,
> but since the bgp always-compare-med command is
> enabled, MED is used in the
> comparison. Entry1 is best of these two entries
> because it has a lower MED.
> Next, entry1 is compared to entry3. The MED is
> checked again because the
> entries are now from the same AS. Entry3 is chosen
> as the best path.
>
> Example 3: bgp deterministic-med Enabled, bgp
> always-compare-med Disabled
> When the bgp deterministic-med command is enabled,
> routes from the
> SAME AS are GROUPED TOGETHER !!!
> There is a group for AS 100 and a group for AS 500.
> The best entries for
> each group are compared
>
> Router compares FROM THE SAME AS FIRST (it reorders
> routes) !!!
>
> Example 4: Both Commands Enabled
> The comparisons in this example would be the same as
> in Example 3, except
> for the last comparison between entry2 and entry1.
> The MED is taken into
> account for the last comparison because the bgp
> always-compare-med command
> is enabled
>
> Dmitry
>
>
> > -----Original Message-----
> > From: Peng Zheng [mailto:zpnist@yahoo.com]
> > Sent: Wednesday, August 28, 2002 11:23 PM
> > To: Nick Shah
> > Cc: ccielab@groupstudy.com
> > Subject: Re: deterministic med
> >
> >
> > But I think no matter how many ASs and paths, the
> > smallest MED will be chosen if bgp
> always-compare-med
> > enabled. Is it right?
> >
> >
> >
> >
> >
> > --- Nick Shah <nshah@connect.com.au> wrote:
> > > Yes, only if using 2 paths, try it with 3 or 4
> > > paths, 2 recd. from ASX and 2
> > > recd. from ASY.
> > >
> > > Nick
> > > ----- Original Message -----
> > > From: "Peng Zheng" <zpnist@yahoo.com>
> > > To: "Nick Shah" <nshah@connect.com.au>
> > > Cc: <ccielab@groupstudy.com>
> > > Sent: Thursday, August 29, 2002 11:51 AM
> > > Subject: Re: deterministic med
> > >
> > >
> > > > I know that. But it's same as I said. Enable
> bgp
> > > > always-compare-med has the same result as
> enable
> > > both.
> > > >
> > > >
> > > > --- Nick Shah <nshah@connect.com.au> wrote:
> > > > > Not sure what you mean here, but.. Consider
> > > this..
> > > > >
> > > > > 192.168.1.0/24 recd. from AS500 MED = 100
> > > > > 192.168.1.0/24 recd. from AS400 MED = 50
> > > > >
> > > > > if BGP deterministic-med is turned on, these
> > > both
> > > > > paths will NOT be chosen
> > > > > based on MED, because they are not from same
> AS.
> > > > >
> > > > > but if BGP always compare MED is turned on,
> then
> > > the
> > > > > path with 50 MED will
> > > > > be selected.
> > > > >
> > > > > rgds
> > > > > ----- Original Message -----
> > > > > From: "Peng Zheng" <zpnist@yahoo.com>
> > > > > To: "Nick Shah" <nshah@connect.com.au>
> > > > > Sent: Thursday, August 29, 2002 10:42 AM
> > > > > Subject: Re: deterministic med
> > > > >
> > > > >
> > > > > > But turn on bgp always-compare-med have
> the
> > > same
> > > > > best
> > > > > > path no matter if turn on bgp
> deterministic
> > > med.
> > > > > Is
> > > > > > that right?
> > > > > >
> > > > > >
> > > > > >
> > > > > > --- Nick Shah <nshah@connect.com.au>
> wrote:
> > > > > > > Jon
> > > > > > >
> > > > > > > I hope you have already read this
> paper..
> > > > > > >
> > > > >
> > >
> http://www.cisco.com/warp/customer/459/bgp-med.html
> > > > > > >
> > > > > > > regardless of that. I will list down the
> > > effect
> > > > > of
> > > > > > > these 2 commands.
> > > > > > >
> > > > > > > * By default (with none of these
> commands
> > > > > entered)
> > > > > > > MED is NOT compared when
> > > > > > > selecting the best path.
> > > > > > > * Turning on bgp deterministic-med,
> turns on
> > > the
> > > > > > > feature to compare MED,
> > > > > > > however it only compares MED, if prefix
> is
> > > > > received
> > > > > > > from same neighbor and
> > > > > > > the best man wins
> > > > > > > * Turning on bgp always-compare-med,
> starts
> > > > > > > comparing 'same prefix' recd.
> > > > > > > from 'different neighbors' and the best
> man
> > > wins
> > > > > > > * Turning on both of them may really not
> be
> > > > > > > required, but it basically
> > > > > > > compares if prefixes are recd. in groups
> of
> > > AS's
> > > > > > > (say same prefix from AS
> > > > > > > 200, via 2 neighbors, and same prefix
> from
> > > AS
> > > > > 100
> > > > > > > via 1 neighbor).
> > > > > > >
> > > > > > > rgds
> > > > > > > Nick
> > > > > > > ----- Original Message -----
> > > > > > > From: "Jon O'Nan"
> <jononan@columbus.rr.com>
> > > > > > > To: <ccielab@groupstudy.com>
> > > > > > > Sent: Thursday, August 29, 2002 8:58 AM
> > > > > > > Subject: deterministic med
> > > > > > >
> > > > > > >
> > > > > > > > Am I correct that:
> > > > > > > >
> > > > > > > > bgp deterministic med - compares med
> > > within
> > > > > AS
> > > > > > > >
> > > > > > > > VS.
> > > > > > > >
> > > > > > > > bgp always-compare-med - compares med
> from
> > > > > another
> > > > > > > AS
> > > > > > > >
> > > > > > > >
> > > > > > > > Thanks
> > > > > > > > Jon
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
>
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