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Problem - OSPF Unequal Cost Load Balancing (Sort of)

 
 
NNTP Reader
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      07-22-2003
I've got a router that plugs in to an ethernet MAN using both a gigabit
ethernet interface and a fast ethernet interface with both interfaces
running OSPF for resiliency.

Because the GigE interface is the faster one, all outbound traffic is taking
that interface outbound from the router. (fine)

The routers at the other end however are MSFC2 cards on our 6500 switches.
Each interface comes in to a different VLAN but the actual speed (bandwidth
descriptor) of each VLAN is the same. This is having the effect of load
balancing the return traffic to the router across both the GigE interface
and the FastE interface.

While it is unlikely that the router will ever see more than 200MB of
sustained traffic, I'd prefer to have the GigE path preferred over the
100meg path. Fudging the bandwidth descriptor on the VLAN isn't an option
because there are other routers in the VLANs that have equal cost
interfaces.

Any ideas ?

= K


 
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Hansang Bae
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Posts: n/a
 
      07-22-2003
In article <(E-Mail Removed)>, http://www.velocityreviews.com/forums/(E-Mail Removed) says...
> I've got a router that plugs in to an ethernet MAN using both a gigabit
> ethernet interface and a fast ethernet interface with both interfaces
> running OSPF for resiliency.
>
> Because the GigE interface is the faster one, all outbound traffic is taking
> that interface outbound from the router. (fine)
>
> The routers at the other end however are MSFC2 cards on our 6500 switches.
> Each interface comes in to a different VLAN but the actual speed (bandwidth
> descriptor) of each VLAN is the same. This is having the effect of load
> balancing the return traffic to the router across both the GigE interface
> and the FastE interface.
>
> While it is unlikely that the router will ever see more than 200MB of
> sustained traffic, I'd prefer to have the GigE path preferred over the
> 100meg path. Fudging the bandwidth descriptor on the VLAN isn't an option
> because there are other routers in the VLANs that have equal cost
> interfaces.



If you can't use BW statement, then I guess "ip ospf priority" is out
too? Unlike BGP, you can't make one particular NLRI/route more
preferable unless you are doing redistribution. It may be ugly, but you
could redistribute the routes at the 6509 side and mark it as an E1
route.

But if they are coming into different VLANs, why can't you use BW or
ospf cost?

--

hsb

"Somehow I imagined this experience would be more rewarding" Calvin
*************** USE ROT13 TO SEE MY EMAIL ADDRESS ****************
************************************************** ******************
Due to the volume of email that I receive, I may not not be able to
reply to emails sent to my account. Please post a followup instead.
************************************************** ******************
 
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NNTP Reader
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Posts: n/a
 
      07-22-2003
I can't use the BW descriptor on the other VLAN because that VLAN also
contains other routers that have interfaces of equal speeds. This is the
only router where the two interfaces are different speeds. Thus I don't want
to change the BW descriptor because equal cost load balancing between the 2
VLAN's is the desired default behavior.

Ideally, there would be something I could tweak at the interface or ospf
config level at the 'deviant' router that would let the upstream routers
know that that path is less desirable.

= K



"Hansang Bae" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> In article <(E-Mail Removed)>, (E-Mail Removed) says...
> > I've got a router that plugs in to an ethernet MAN using both a gigabit
> > ethernet interface and a fast ethernet interface with both interfaces
> > running OSPF for resiliency.
> >
> > Because the GigE interface is the faster one, all outbound traffic is

taking
> > that interface outbound from the router. (fine)
> >
> > The routers at the other end however are MSFC2 cards on our 6500

switches.
> > Each interface comes in to a different VLAN but the actual speed

(bandwidth
> > descriptor) of each VLAN is the same. This is having the effect of load
> > balancing the return traffic to the router across both the GigE

interface
> > and the FastE interface.
> >
> > While it is unlikely that the router will ever see more than 200MB of
> > sustained traffic, I'd prefer to have the GigE path preferred over the
> > 100meg path. Fudging the bandwidth descriptor on the VLAN isn't an

option
> > because there are other routers in the VLANs that have equal cost
> > interfaces.

>
>
> If you can't use BW statement, then I guess "ip ospf priority" is out
> too? Unlike BGP, you can't make one particular NLRI/route more
> preferable unless you are doing redistribution. It may be ugly, but you
> could redistribute the routes at the 6509 side and mark it as an E1
> route.
>
> But if they are coming into different VLANs, why can't you use BW or
> ospf cost?
>
> --
>
> hsb
>
> "Somehow I imagined this experience would be more rewarding" Calvin
> *************** USE ROT13 TO SEE MY EMAIL ADDRESS ****************
> ************************************************** ******************
> Due to the volume of email that I receive, I may not not be able to
> reply to emails sent to my account. Please post a followup instead.
> ************************************************** ******************



 
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NNTP Reader
Guest
Posts: n/a
 
      07-23-2003
I don't see how adjusting the cost is going to change anything. The router
with the 2 interfaces already knows that the GigE is faster than the 100meg
interface and uses the GigE outbound.

The problem is that the return trip from the MSFCs are load balancing across
the 2 VLAN's because the VLAN interface speed is the same. It would be nice
if the MSFC's could determine that the particular neighbor on VLAN B
established its relationship via a slower interface than the same neighbor
on VLAN C but this doesn't seem to be the case.

= K

"shope" <(E-Mail Removed)> wrote in message
news:itsTa.83$(E-Mail Removed)...
> "NNTP Reader" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> > I can't use the BW descriptor on the other VLAN because that VLAN also
> > contains other routers that have interfaces of equal speeds. This is the
> > only router where the two interfaces are different speeds. Thus I don't

> want
> > to change the BW descriptor because equal cost load balancing between

the
> 2
> > VLAN's is the desired default behavior.
> >
> > Ideally, there would be something I could tweak at the interface or ospf
> > config level at the 'deviant' router that would let the upstream routers
> > know that that path is less desirable.

>
> The OSPF cost on a cisco router is set by default from the bandwidth of

the
> interface - but you can set the cost manually on an interface to override
> that.
>
> Seems the simplest way really since it wont have side effects for other
> things.
> >
> > = K
> >
> >
> >
> > "Hansang Bae" <(E-Mail Removed)> wrote in message
> > news:(E-Mail Removed)...
> > > In article <(E-Mail Removed)>, (E-Mail Removed) says...
> > > > I've got a router that plugs in to an ethernet MAN using both a

> gigabit
> > > > ethernet interface and a fast ethernet interface with both

interfaces
> > > > running OSPF for resiliency.
> > > >
> > > > Because the GigE interface is the faster one, all outbound traffic

is
> > taking
> > > > that interface outbound from the router. (fine)
> > > >
> > > > The routers at the other end however are MSFC2 cards on our 6500

> > switches.
> > > > Each interface comes in to a different VLAN but the actual speed

> > (bandwidth
> > > > descriptor) of each VLAN is the same. This is having the effect of

> load
> > > > balancing the return traffic to the router across both the GigE

> > interface
> > > > and the FastE interface.
> > > >
> > > > While it is unlikely that the router will ever see more than 200MB

of
> > > > sustained traffic, I'd prefer to have the GigE path preferred over

the
> > > > 100meg path. Fudging the bandwidth descriptor on the VLAN isn't an

> > option
> > > > because there are other routers in the VLANs that have equal cost
> > > > interfaces.
> > >
> > >
> > > If you can't use BW statement, then I guess "ip ospf priority" is out
> > > too? Unlike BGP, you can't make one particular NLRI/route more
> > > preferable unless you are doing redistribution. It may be ugly, but

you
> > > could redistribute the routes at the 6509 side and mark it as an E1
> > > route.
> > >
> > > But if they are coming into different VLANs, why can't you use BW or
> > > ospf cost?
> > >
> > > --
> > >
> > > hsb
> > >
> > > "Somehow I imagined this experience would be more rewarding" Calvin
> > > *************** USE ROT13 TO SEE MY EMAIL ADDRESS ****************
> > > ************************************************** ******************
> > > Due to the volume of email that I receive, I may not not be able to
> > > reply to emails sent to my account. Please post a followup instead.
> > > ************************************************** ******************

> --
> Regards
>
> Stephen Hope - remove xx from email to reply
>
>



 
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shope
Guest
Posts: n/a
 
      07-23-2003


"NNTP Reader" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I don't see how adjusting the cost is going to change anything. The router
> with the 2 interfaces already knows that the GigE is faster than the

100meg
> interface and uses the GigE outbound.


The router may "know" the speeds of the interfaces or not - MSFCs usually
talk to VLANs rather than ports.

If the network was directly connected you would be right - but here it
learns via OSPF and the OSPF interface costs affect the cost to the
destination

So the OSPF costs dictate which routes are preferred - so if you override
the default cost you can bias the traffic to go out of a specific interface.
>
> The problem is that the return trip from the MSFCs are load balancing

across
> the 2 VLAN's because the VLAN interface speed is the same. It would be

nice
> if the MSFC's could determine that the particular neighbor on VLAN B
> established its relationship via a slower interface than the same neighbor
> on VLAN C but this doesn't seem to be the case.


There is another way you could try - makr the slower interface as "passive"
in the config, and OSPF wont find the neighbour and build an ajacency, so
wont learn any routes via that interface.

I dont think this is what you wanted, since this would prevent you having
this path as a backup link.
>
> = K
>
> "shope" <(E-Mail Removed)> wrote in message
> news:itsTa.83$(E-Mail Removed)...
> > "NNTP Reader" <(E-Mail Removed)> wrote in message
> > news:(E-Mail Removed)...
> > > I can't use the BW descriptor on the other VLAN because that VLAN also
> > > contains other routers that have interfaces of equal speeds. This is

the
> > > only router where the two interfaces are different speeds. Thus I

don't
> > want
> > > to change the BW descriptor because equal cost load balancing between

> the
> > 2
> > > VLAN's is the desired default behavior.
> > >
> > > Ideally, there would be something I could tweak at the interface or

ospf
> > > config level at the 'deviant' router that would let the upstream

routers
> > > know that that path is less desirable.

> >
> > The OSPF cost on a cisco router is set by default from the bandwidth of

> the
> > interface - but you can set the cost manually on an interface to

override
> > that.
> >
> > Seems the simplest way really since it wont have side effects for other
> > things.
> > >
> > > = K
> > >
> > >
> > >
> > > "Hansang Bae" <(E-Mail Removed)> wrote in message
> > > news:(E-Mail Removed)...
> > > > In article <(E-Mail Removed)>, (E-Mail Removed) says...
> > > > > I've got a router that plugs in to an ethernet MAN using both a

> > gigabit
> > > > > ethernet interface and a fast ethernet interface with both

> interfaces
> > > > > running OSPF for resiliency.
> > > > >
> > > > > Because the GigE interface is the faster one, all outbound traffic

> is
> > > taking
> > > > > that interface outbound from the router. (fine)
> > > > >
> > > > > The routers at the other end however are MSFC2 cards on our 6500
> > > switches.
> > > > > Each interface comes in to a different VLAN but the actual speed
> > > (bandwidth
> > > > > descriptor) of each VLAN is the same. This is having the effect of

> > load
> > > > > balancing the return traffic to the router across both the GigE
> > > interface
> > > > > and the FastE interface.
> > > > >
> > > > > While it is unlikely that the router will ever see more than 200MB

> of
> > > > > sustained traffic, I'd prefer to have the GigE path preferred over

> the
> > > > > 100meg path. Fudging the bandwidth descriptor on the VLAN isn't an
> > > option
> > > > > because there are other routers in the VLANs that have equal cost
> > > > > interfaces.
> > > >
> > > >
> > > > If you can't use BW statement, then I guess "ip ospf priority" is

out
> > > > too? Unlike BGP, you can't make one particular NLRI/route more
> > > > preferable unless you are doing redistribution. It may be ugly, but

> you
> > > > could redistribute the routes at the 6509 side and mark it as an E1
> > > > route.
> > > >
> > > > But if they are coming into different VLANs, why can't you use BW or
> > > > ospf cost?
> > > >
> > > > --
> > > >
> > > > hsb
> > > >
> > > > "Somehow I imagined this experience would be more rewarding" Calvin
> > > > *************** USE ROT13 TO SEE MY EMAIL ADDRESS ****************
> > > > ************************************************** ******************
> > > > Due to the volume of email that I receive, I may not not be able to
> > > > reply to emails sent to my account. Please post a followup instead.
> > > > ************************************************** ******************

> > --
> > Regards
> >
> > Stephen Hope - remove xx from email to reply

--
Regards

Stephen Hope - remove xx from email to reply


 
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Harri Suomalainen
Guest
Posts: n/a
 
      07-24-2003
NNTP Reader <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I don't see how adjusting the cost is going to change anything. The router
> with the 2 interfaces already knows that the GigE is faster than the

100meg
> interface and uses the GigE outbound.
>
> The problem is that the return trip from the MSFCs are load balancing

across
> the 2 VLAN's because the VLAN interface speed is the same. It would be

nice
> if the MSFC's could determine that the particular neighbor on VLAN B
> established its relationship via a slower interface than the same neighbor
> on VLAN C but this doesn't seem to be the case.


Consider the outbound traffic from MSFC. If the interface speeds are same
for that it will make no difference (for the msfc) which interface is being
used.
This is how routing works, avoiding secondary effects is not the purpose
of routing, only the selection of a good route is.

However, you seem to be trying to solve a secondary problem for avoiding
overloading the next hop. The next-hop cannot influece the routing of MSFC.
I think BGP is the only routing protocol with which you can influece how
the neighbor will route the traffic *to you*. All other protocols make only
choices for how you route the traffic out of your local node for a shortest
possible route in you local nodes point of view.

OSPF cost can be used as a static solution. Add a worse (or better) cost
for one VLAN on both of your MSFCs and they will prefer the vlan with
better cost. (Pain to administer and maintain if you have lots of nodes.)

However, this leads to another problem: all the traffic is routed through
the
better vlan now and the other vlan is idling with no traffic. I guess from
the
previous that this means routing all through a single 100Mbit interface out
of the MSFC. This might or might not be acceptable.

Simple solution for unequal load balancing with OSPF:

Have vlan A & B on a gig-interface and VLAN C on the 100M interface.
If outbound costs are equal this will mean equal load balancing for vlans
A,B,C. Of this total traffic 2/3 will be on the gigE and 1/3 on the
FastEthernet
because the VLAN distribution.

This means adding more vlans but can be used for a sort of unequal load
balancing which works with complete support of the routeing protocol.
All you need to do is to engineer suitable number of neighboring interfaces.
--
Harri


 
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Harri Suomalainen
Guest
Posts: n/a
 
      07-24-2003
NNTP Reader <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I don't see how adjusting the cost is going to change anything. The router
> with the 2 interfaces already knows that the GigE is faster than the

100meg
> interface and uses the GigE outbound.
>
> The problem is that the return trip from the MSFCs are load balancing

across
> the 2 VLAN's because the VLAN interface speed is the same. It would be

nice
> if the MSFC's could determine that the particular neighbor on VLAN B
> established its relationship via a slower interface than the same neighbor
> on VLAN C but this doesn't seem to be the case.


Consider the outbound traffic from MSFC. If the interface speeds are same
for that it will make no difference (for the msfc) which interface is being
used.
This is how routing works, avoiding secondary effects is not the purpose
of routing, only the selection of a good route is.

However, you seem to be trying to solve a secondary problem for avoiding
overloading the next hop. The next-hop cannot influece the routing of MSFC.
I think BGP is the only routing protocol with which you can influece how
the neighbor will route the traffic *to you*. All other protocols make only
choices for how you route the traffic out of your local node for a shortest
possible route in you local nodes point of view.

OSPF cost can be used as a static solution. Add a worse (or better) cost
for one VLAN on both of your MSFCs and they will prefer the vlan with
better cost. (Pain to administer and maintain if you have lots of nodes.)

However, this leads to another problem: all the traffic is routed through
the
better vlan now and the other vlan is idling with no traffic. I guess from
the
previous that this means routing all through a single 100Mbit interface out
of the MSFC. This might or might not be acceptable.

Simple solution for unequal load balancing with OSPF:

Have vlan A & B on a gig-interface and VLAN C on the 100M interface.
If outbound costs are equal this will mean equal load balancing for vlans
A,B,C. Of this total traffic 2/3 will be on the gigE and 1/3 on the
FastEthernet
because the VLAN distribution.

This means adding more vlans but can be used for a sort of unequal load
balancing which works with complete support of the routeing protocol.
All you need to do is to engineer suitable number of neighboring interfaces.
--
Harri


 
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newsreader
Guest
Posts: n/a
 
      07-25-2003
How about EIGRP with variance? If you're all Cisco, perhaps you could try
that...

"NNTP Reader" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I've got a router that plugs in to an ethernet MAN using both a gigabit
> ethernet interface and a fast ethernet interface with both interfaces
> running OSPF for resiliency.
>
> Because the GigE interface is the faster one, all outbound traffic is

taking
> that interface outbound from the router. (fine)
>
> The routers at the other end however are MSFC2 cards on our 6500 switches.
> Each interface comes in to a different VLAN but the actual speed

(bandwidth
> descriptor) of each VLAN is the same. This is having the effect of load
> balancing the return traffic to the router across both the GigE interface
> and the FastE interface.
>
> While it is unlikely that the router will ever see more than 200MB of
> sustained traffic, I'd prefer to have the GigE path preferred over the
> 100meg path. Fudging the bandwidth descriptor on the VLAN isn't an option
> because there are other routers in the VLANs that have equal cost
> interfaces.
>
> Any ideas ?
>
> = K
>
>



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