Velocity Reviews - Computer Hardware Reviews

Velocity Reviews > Newsgroups > Computing > Cisco > Load-balancing across four T1's on 2 routers

Reply
Thread Tools

Load-balancing across four T1's on 2 routers

 
 
Sean-Usenet
Guest
Posts: n/a
 
      08-31-2006
The ISP's routers will be ABRs, and our area will be configured as a
totally stubby network. Because of that the ABR will automatically
inject the default routes into our area.

Merv wrote:
> What is the origin of default route on each 2800 ?
>
> Is it provided by the ISP via a dynamic routing protocol ?
>
> Or is it via static routes configured on the 2800 ?


 
Reply With Quote
 
 
 
 
Sean-Usenet
Guest
Posts: n/a
 
      08-31-2006
Hi again Merv, thanks for helping me out with this.

Yea, i understand that by default CEF is per desination-source, but
there is an option to switch it to per packet, which we may use.

Merv wrote:
> > We do not plan on using MLPPP.

>
> That being the case and assuming you will be using CEF, be aware that
> the two T1 will not be evenly load balanced in real time as CEF does
> per destination load balancing.


 
Reply With Quote
 
 
 
 
Nathan Harmon
Guest
Posts: n/a
 
      08-31-2006
Sean-Usenet wrote:
> I am setting up the following:
>
> - 2 Cisco 2800 series routers, each has two T-1 internet connections.
> - Those 2 routers are also connected to a 100mb layer-3 switch.
> - Our firewall will also connected to that layer-3 switch.
> - The firewall's' default gateway will be that layer-3 switch.
> - The workstations are behind the firewall, and will use the firewall
> as their default gateway


Well, if I were setting this up, I'm not sure I would need to use the
multilayer capabilities of the layer-3 switch. Is the Cisco 2800
capable of GLBP? If so, I would set up GLBP on both of the routers, and
make the load-balanced gateway address the default route for the
firewall. And then the routers can weigh their traffic capabilities and
load balance themselves.

Merv does bring up a good point about needing to mitigate the effects
of the ISP losing connectivity.

 
Reply With Quote
 
Merv
Guest
Posts: n/a
 
      08-31-2006

BTW is it one ISP or two ?

 
Reply With Quote
 
Sean-Usenet
Guest
Posts: n/a
 
      08-31-2006
Hi Nathan

I looked a little at using GLBP, but I was concerned about how well it
would load-balance, since all traffic is going through the firewall.

- When the firewall receives its first packet, it will ARP for the mac
of the default gateway
- The GLBP AVG will respond to the arp request with the virtual mac of
itself or the other router
- Then the firewall will add this arp response it its arp cache and
forward the data packet
- Since the arp response is now stored in the firewall's arp cache, it
will not arp again until it expires, thus it will continue to use the
same router

In other words, GLBP load-balances on a per source host basis, and
unfortunetly becaues of the firewall there is only 1 host.

Does that make sense, or is my logic off somewhere?


Nathan Harmon wrote:
> Sean-Usenet wrote:
> > I am setting up the following:
> >
> > - 2 Cisco 2800 series routers, each has two T-1 internet connections.
> > - Those 2 routers are also connected to a 100mb layer-3 switch.
> > - Our firewall will also connected to that layer-3 switch.
> > - The firewall's' default gateway will be that layer-3 switch.
> > - The workstations are behind the firewall, and will use the firewall
> > as their default gateway

>
> Well, if I were setting this up, I'm not sure I would need to use the
> multilayer capabilities of the layer-3 switch. Is the Cisco 2800
> capable of GLBP? If so, I would set up GLBP on both of the routers, and
> make the load-balanced gateway address the default route for the
> firewall. And then the routers can weigh their traffic capabilities and
> load balance themselves.
>
> Merv does bring up a good point about needing to mitigate the effects
> of the ISP losing connectivity.


 
Reply With Quote
 
Sean-Usenet
Guest
Posts: n/a
 
      08-31-2006
It is the same ISP

Merv wrote:
> BTW is it one ISP or two ?


 
Reply With Quote
 
Sean-Usenet
Guest
Posts: n/a
 
      08-31-2006
If one of the two ISP routers does come partitioned (eg. its FE port
fails) won't it stop sending a default route down the T1s to us?

Since the ISPs routers are configured as ABR and our area is a totally
stubby area, the ISPs routers will send a default route to us
automatically. Will the ISP's router continue to send a default route
even though all its other interfaces are down?


The traffic will be load-balanced across the pair of T1s via equal-cost
load-balancing because of OSPF


Merv wrote:
> There may be some additional things to consider ...
>
> What happens if an ISP upstream router becomes partitiononed from the
> rest of the ISP network - the T1 will stay up but your traffic will be
> blackholed - believe it happens.
>
> Also what approach is being planned to load balance the traffic across
> each of the pairs of T1s ?


 
Reply With Quote
 
nakhmanson@gmail.com
Guest
Posts: n/a
 
      08-31-2006

Sean-Usenet wrote:
> It is the same ISP
>
> Merv wrote:
> > BTW is it one ISP or two ?


Sean

I am sorry for stupid question, but I just can't resist. WHY all that
hustle with 4 T1's without MLPP, 2 routers + OSPF, if you have just ONE
provider. As far as I understand, you are trying to "invent the wheel",
which is design "indestructible" Internet access, or am I wrong? If
not, then WHY you want a SINGLE L3 switch (which you don't need) +
SINGLE firewall?

Roman

 
Reply With Quote
 
Sean-Usenet
Guest
Posts: n/a
 
      08-31-2006
Haha, well I dumbed down the full setup a little bit for simplicity
sake.

It is actually not a single L3 switch, it is two L3 switches with
redundant 32Gbps interconnects between them. With 1 router going to
each switch. The L3 switch is needed because the firewall is not setup
to run OSPF.

The firewall is not a single firewall, it is an active/passive firewall
cluster. One firewall connects to one of the above L3 switches and one
firewall connects to the other L3 switch.

Here is the reason for not using MLPP:

If all four T1s are up, everything would work fine with MLPP. Each
router would see a 3Mb connection. The L3 switch would have 2 default
routes in its routing table, and perform equal-cost load-balancing.
The traffic would also load-balance very nicely across the T1s because
of MLPP.

The problem is if we lose one T1. At that point, one router has a
1.5Mb connection and the other still has a 3Mb connection. The L3
switch will then see 2 UN-equal cost default routes in its routing
table. Because they are not equal-cost routes, all traffic would be
directed to the router that has two operational T1s. The end result is
the same as loosing two T1s even though we only lost 1. OSPF only
performs equal-cost load-balancing.

Without using MLPP, the L3 switch will still see two equal-cost default
routes and route traffic to both routers. Unless of course a router
looses both T1s, then it won't receive any traffic since it won't be
passing along the default route from the ABR any longer.

The reason for using a L3 switch and not GLBP on the routers is because
GLBP load-balances on a per source-host basis. Since the source host
is always the firewall, the traffic will always go through the same
router.
http://www.cisco.com/univercd/cc/td/...15/ft_glbp.htm


Now that I answered your question, any help with mine?

Thanks
Sean


http://www.velocityreviews.com/forums/(E-Mail Removed) wrote:
> Sean-Usenet wrote:
> > It is the same ISP
> >
> > Merv wrote:
> > > BTW is it one ISP or two ?

>
> Sean
>
> I am sorry for stupid question, but I just can't resist. WHY all that
> hustle with 4 T1's without MLPP, 2 routers + OSPF, if you have just ONE
> provider. As far as I understand, you are trying to "invent the wheel",
> which is design "indestructible" Internet access, or am I wrong? If
> not, then WHY you want a SINGLE L3 switch (which you don't need) +
> SINGLE firewall?
>
> Roman


 
Reply With Quote
 
Sean-Usenet
Guest
Posts: n/a
 
      08-31-2006
Hi James

Thanks for the response.

Actually the L3 switch will only see 2 equal-cost routes. The L3
switch will show the 1 default route with a next hop of 1 router and a
2nd default route with a next hop of the other router.

I mocked this up in my lab to be 100% sure. Although, it would have
been great if the L3 switch did see 4 routes!

Sean

James wrote:
> I am 99% sure that your layer three switch will see four equal cost
> routes not two, when one T1 goes down it will then see three routes.
> Your layer three switch will take this into consideration when making
> its balancing decision.
>
> James
>
>
> Igor Mamuzic wrote:
> > Maybe you could find solution on one of these links:
> > - if you have 12.3 IOS see:
> > http://www.cisco.com/en/US/products/...0801d1e95.html
> > or
> > - if you have 12.4 IOS see:
> > http://www.cisco.com/en/US/products/...0801d1e95.html
> >
> >
> > B.R.
> > Igor
> >
> >
> >
> > "Sean-Usenet" <(E-Mail Removed)> wrote in message
> > news:(E-Mail Removed) oups.com...
> > >I am setting up the following:
> > >
> > > - 2 Cisco 2800 series routers, each has two T-1 internet connections.
> > > - Those 2 routers are also connected to a 100mb layer-3 switch.
> > > - Our firewall will also connected to that layer-3 switch.
> > > - The firewall's' default gateway will be that layer-3 switch.
> > > - The workstations are behind the firewall, and will use the firewall
> > > as their default gateway
> > >
> > > - OSPF will be running on the 2 routers and the layer-3 switch, and
> > > also on 2 routers on the ISP's site.
> > > - The OSPF area will be Totally Stubby, thus the ISP's routers will be
> > > advertising default routes into our network.
> > >
> > > As long as all four T-1's are up, everything should work fine:
> > >
> > > - The workstations will route outbound packets to the firewall
> > > - The firewall will route the packets to the layer-3 switch
> > > - The layer-3 switch is running OSPF and will see two equal cost
> > > default routes, and will load-balance traffic between our two routers
> > > - The routers will in turn also have two defaults routes (1 route
> > > through each T-1), and load-balance traffic across each T-1
> > >
> > >
> > > My problem is what happens when one T-1 goes down? Our layer-3 switch
> > > will still see equal cost routes and split the traffic across the two
> > > routers, even though one router has 1/2 the bandwidth.
> > >
> > > Can someone help me with this problem? Please let me know if you have
> > > any questions on what I explained above! Here is a diagram of the
> > > setup, i hope it looks ok:
> > >
> > > R1 R2 (ISP Routers)
> > > || ||
> > > || || (4 total T-1s)
> > > || ||
> > > R1 R2 (Our Routers)
> > > | |
> > > \ /
> > > \ /
> > > \ /
> > > Layer-3
> > > Switch
> > > |
> > > |
> > > |
> > > Firewall
> > > |
> > > |
> > > |
> > > Layer-2
> > > Switch
> > > |
> > > |
> > > |
> > > |
> > > Workstations
> > >
> > >
> > > Thanks!
> > > Sean
> > >


 
Reply With Quote
 
 
 
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Four Networks, two routers Riemann5334 General Computer Support 0 02-11-2013 11:49 PM
New Canon EIS mirrorless system - Four Thirds, but not Four Thirds! Bruce Digital Photography 31 09-25-2010 05:38 AM
DHCP across routers lelo Cisco 2 11-28-2005 02:48 AM
cisco routers and netgear routers Jon L. Miller Cisco 2 02-05-2005 02:49 AM
Connect 2 routers (wireless and regular routers) Dineyar Buhariwala Wireless Networking 1 11-24-2004 01:37 PM



Advertisments