load sharing

[heshamderbala]

Hi
i have 2 switches 2620 and 2 modems connecting this site to the remote site which have the same items the customer need to make the 2 links load balanced as when one link goes down the user on any of the 2 switches dont interupted please advice what configuration have to be done bearing in mind 2 links have to move traffic balanced as no one is redundant to the other
Thanks
Please reply ASAP

[Vince_Whirlwind]

Who still uses modems?

You would need routers running a routing protocol, say OSPF, on either side of the link.

[heshamderbala]

He has got an old microwave links point to point as the 2 modems has got another 2 in the other site please consider that we could use two 3500yl with premium license instead of the two 2620 in both sites
Thanks

[Vince_Whirlwind]

Depending on the nature of the links, you could simply link-aggregate the two links. If you have a good number of devices on either side, then this could give you OK "random" load-balancing.

Otherwise, the 3500 is a pretty powerful layer-3 switch and can run OSPF. Create each link as a point-to-point routed link and enable OSPF.

SiteARouter

int vlan 10 name DATA ip address 10.10.10.1/24

int vlan 101 ip address 10.10.101.1/24

int vlan 102 ip address 10.10.102.1/24

router ospf 1

network 10.10.101.0 0.0.0.255 area 0

network 10.10.101.0 0.0.0.255 area 0

network 10.10.10.0 0.0.0.255 area 0

SiteBRouter

int vlan 20 name DATA ip address 10.10.20.1/24

int vlan 101 ip address 10.10.101.2/24

int vlan 102 ip address 10.10.102.2/24

router ospf 1

network 10.10.101.0 0.0.0.255 area 0

network 10.10.101.0 0.0.0.255 area 0

network 10.10.20.0 0.0.0.255 area 0

[heshamderbala]

Sorry i dont get it we have 2 switches in each site did you mean i have to do the configuration on the 2 switches as site A switch is not linked locally to the other switch on site A if yes there is no load sharin on links as users comming out from first switch in site A will not routed to second switch in site A when link of first modem that is connected to first switch in Site A goes down
And please advice what is the default gateway of users in each site.
Also how to make the two modems link aggregated with each other if we use your first solution

Thanks

[Vince_Whirlwind]

For simple link aggregation, I don't know what these modems are or how they work, but if your switches on either Site can see each other at Layer2 (ie, the modems provide some kind of ethernet bridge), then aggregate their facing interfaces.

If you go the routed option, you configure the two switches as layer-3 switches that face each other across the link. If you have any other layer-3 devices on each site, you will need to inform them how to route to the other site by giving them a route to the switch that is providing the link.

I'm not sure I understand your topology, but let's assume:

SiteA: 10.10.10.0/24

SiteB: 10.10.20.0/24

On SiteA you have RadioLinkSwitchA.

On SiteB you have RadioLinkSwitchB.

Somewhere on SiteA, your devices in 10.10.10.0 have their "default Gateway". That is the router for that site/subnet. If that router is on RadioLinkSwitchA, then it all works. If that default GW is on AnotherRouterA, then (for example) configure AnotherRouterA with a static route:

10.10.20.0-->RadioLinkSwitchA.

[Arimo]

Hi

If I am reading this correctly, the topology your customer wants is:

SiteA_switch_1  ->  modem1  ->  SiteB_switch_1

SiteA_switch_2  ->  modem2  ->  SiteB_switch_2

There's no way to aggregate the link. If the topology looks like this:

SiteA_switch1_port1  ->  modem1  ->  SiteB_switch1_port1

SiteA_switch1_port2  ->  modem2  ->  SiteB_switch1_port2

... aggregation _may_ be possible. I doubt it, but then again I've never tested aggregating this kind of WAN link.

If this works and modem 1 goes down, the client traffic will be routed through modem 2. However when both links are up, there's no load balancing. LACP doesn't contain a method for that.

Redundancy is possible, but only with 3500s. To do that you use the first topology, 2 switches on both sites. You configure the switches on SiteA to be VRRP partners, and do the same for switches in SiteB. The switches on both sites will have a virtual IP address, which acts as the gateway. However, again, there is no load balancing by default. You can manually add some load balancing depending on the way you configure your VRRP.

[heshamderbala]

Hi

Actually the topology is as follows:

Site A Switch1_port1  ->  modem1  ->  SiteB_Modem1---switch1_port1

Site A Switch2_port1  ->  modem2  ->  SiteB_Modem2---switch2_port1

This Means that in Site A when modem 1  fails packets automatically pass through modem 2 without any losses in packets and also load balance between two lines has to be acheived as one packet pass through modem 1 and the other packet pass through modem 2

For the VRRP will not work in this scenario as one link will be up and the other will be down

For the OSPF iam not sure it will work so please send me more detailed configuration as in your previous post you mentioned one switch at a site and this is not the case.

Thanks

[Arimo]

Hi

That's what I thought. You cannot aggregate this setup at all.

Whether or not one link will be down using VRRP depends completely how you configure it. Do both sites also use the modems for Internet connectivity, or is it strictly a link between the two sites and Internet connectivity is done with a separate router?

[heshamderbala]

Hi

First for the VRRP when you configure it the master switch is the leader and the virtual ip address is the default gateway and the master switch is tracking the track port which is the port the modem on it and when that port is down then automatically the backup switch converted to master and will pass traffic of users to the modems it has in its tracking

and with respect to the internet there is no internet on these modems it is used for this purpose only

Thanks

[Arimo]

Hey again

You are correct about the way VRRP works. However please note that you do not configure one global VRRP master/backup. You convigure them by VLAN. Switch1 is VRRP master for VLAN 10 and backup for VLANs 20, Switch2 is VRRP master for VLAN 20 and backup for VLAN 10. When both switches are up'n running, both switches will be utilized.

[heshamderbala]

Hi

Please see attached as i tried this scenario on paper and it doesnt work how the user will be connected to this network is it in vlan 10 or 20 on any of the switches and what is his default gateway 

please advice

Thanks