Mailing List Archive: OSPF Metric in Juniper.

OSPF Metric in Juniper.

Jan 21, 2004, 5:04 AM

Post #1 of 4 (2027 views)

Dear All,
Kindly help in finding the method used for calculating OSPF metric for
Juniper Router in the following scenario.

Router A & B are in same location connected via Gigabit link shown in blue.
All the routers are in OSPF area 0 & traffic-engineering has enabled on the
same.
All other links are STM1, shown in red.

Router A ----- ------ Router C
| |
| |
Router B ----- ------ Router D

When we issue ping from Router A to Router D, ideally as per OSPF metric
which is cost, it should follow the "Router B & Router D" path, but it is
following "Router C & Router D"
What could be the reason of taking path which are having both STM1 links,
instead of Gigabit & STM1 path?

Thanks / Milind.

OSPF Metric in Juniper. [ In reply to ]

lerik at nolink

Jan 21, 2004, 5:25 AM

Post #2 of 4 (1998 views)

Permalink

On Wed, 2004-01-21 at 11:04, Milind Deshpande wrote:

[snip]
> When we issue ping from Router A to Router D, ideally as per OSPF metric
> which is cost, it should follow the "Router B & Router D" path, but it is
> following "Router C & Router D"
> What could be the reason of taking path which are having both STM1 links,
> instead of Gigabit & STM1 path?

Unless you have increased the OSPF reference bandwidth in your network
or manually assigned metrics to interfaces, anything >= 100Mbit has a
metric of 1 (100Mbit is the default reference-bandwidth for OSPF cost
calculation). Which means A-C-D and A-B-D are equal-cost paths (same
number of hops, all hops are metric 1). Then router A will load-balance
between the two, a "show route <ip of D>" should show you both paths.

/leg

OSPF Metric in Juniper. [ In reply to ]

bradd at eng

Jan 21, 2004, 5:29 AM

Post #3 of 4 (1995 views)

Permalink

On Wed, Jan 21, 2004 at 11:24:59AM +0100, Lars Erik Gullerud wrote:
> On Wed, 2004-01-21 at 11:04, Milind Deshpande wrote:
>
> [snip]
> > When we issue ping from Router A to Router D, ideally as per OSPF metric
> > which is cost, it should follow the "Router B & Router D" path, but it is
> > following "Router C & Router D"
> > What could be the reason of taking path which are having both STM1 links,
> > instead of Gigabit & STM1 path?
>
> Unless you have increased the OSPF reference bandwidth in your network
> or manually assigned metrics to interfaces, anything >= 100Mbit has a
> metric of 1 (100Mbit is the default reference-bandwidth for OSPF cost
> calculation). Which means A-C-D and A-B-D are equal-cost paths (same
> number of hops, all hops are metric 1). Then router A will load-balance
> between the two, a "show route <ip of D>" should show you both paths.

yea you'd think traffic would be load balanced...according to this anyways:
http://www.juniper.net/techpubs/software/junos/junos61/swconfig61-routing/html/ospf-config17.html#1014485

i wonder what effect having traffic-engineering shortcuts enabled
will have though.hmmmm...

-b

>
> /leg
>
>
> _______________________________________________
> juniper-nsp mailing list juniper-nsp@puck.nether.net
> http://puck.nether.net/mailman/listinfo/juniper-nsp

OSPF Metric in Juniper. [ In reply to ]

web at typo

Jan 21, 2004, 2:27 PM

Post #4 of 4 (1996 views)

Permalink

On Wed, Jan 21, 2004 at 05:24:45AM -0500, brad dreisbach wrote:
> On Wed, Jan 21, 2004 at 11:24:59AM +0100, Lars Erik Gullerud wrote:
> > On Wed, 2004-01-21 at 11:04, Milind Deshpande wrote:
> >
> > [snip]
> > > When we issue ping from Router A to Router D, ideally as per OSPF metric
> > > which is cost, it should follow the "Router B & Router D" path, but it is
> > > following "Router C & Router D"
> > > What could be the reason of taking path which are having both STM1 links,
> > > instead of Gigabit & STM1 path?
> >
> > Unless you have increased the OSPF reference bandwidth in your network
> > or manually assigned metrics to interfaces, anything >= 100Mbit has a
> > metric of 1 (100Mbit is the default reference-bandwidth for OSPF cost
> > calculation). Which means A-C-D and A-B-D are equal-cost paths (same
> > number of hops, all hops are metric 1). Then router A will load-balance
> > between the two, a "show route <ip of D>" should show you both paths.
>
> yea you'd think traffic would be load balanced...according to this anyways:
> http://www.juniper.net/techpubs/software/junos/junos61/swconfig61-routing/html/ospf-config17.html#1014485
>
> i wonder what effect having traffic-engineering shortcuts enabled
> will have though.hmmmm...

Except that according to the documentaiton I've seen (and noted
behaviors from experience), even per-packet load balancing is per-flow
(after a fashion at least). So seeing it take only one path does not
surprise me.

---
Wayne Bouchard
web@typo.org
Network Dude
http://www.typo.org/~web/