STP or OSPF Redundency ?

[ahmedssk]

I have to link 3 sites (A,B,C) using fiber optic link and microwave link (mesh topology) as a backup link , Im thinking of creating three vlans one for each siteand route between them, then what about redundency shall I use OSPF routing or STP to reach ultimate level of availiblity?

the link is as flows

1)Fiber

Site A---Fo---site B---FO---Site C

2)MicroWave (mesh toplogy)

Site A---Mw---Site B---Mw---Site C

Site A-----------MW----------Site C

Site B----------MW-----------Site C

3) Gears

SitA---------SiteB-----------SiteC

4500 ------- 4500 -------- 3750

[vijayasankar]

Hi,

It depends on your requirements.

Are you going to span vlans across these 3 sites ?

Only if you are going to span vlans across these sites, you need to STP to take care about Layer 2 redundancy.

If you are going to have local vlans on all these three site and going to route between them, then use a routing protocol like OSPF/EIGRP to take care about link redundancy.

Hope this helps.

-VJ

[ahmedssk]

hi VJ

I'm going to span vlans between 2 sites A and B and make local vlans in site C, what do you think, the bandwidth of Microwave link is 34Mbps, so would this prevent me from creating trunk between site A and B?

[Ahmede]

Not sure about your exact setup, but the network designs I created lately I was using OSPF redundancy and get rid of the STP.. STP is too much headache..

[brunop]

One consideration is link usage and disaster recovery. STP will block any redundant links meaning that bandwidth is unused. You can work around this by making one link the root-bridge for vlan one, the second for vlan two and so on, however.

Another consideration is fail-over, with OSPF you can have all of your links ‘live’ and passing traffic and a link failure should be of minimal impact. Using layer-2 links, you will have to wait for the STP timers to notice the link is down and unblock before they begin passing traffic. This can also tuned with some of the newer STP protocols and timers but this is another thing to manage.

Finally there are just general design considerations. Do you have to have a layer-2 link? How many hosts do you expect? How big a broadcast domain will this create? How much control of the hosts will you have? Will you be able to prevent large amounts of broadcast and multicast traffic?

[ahmedssk]

HI brunop,,

I'm going to span vlans between 2 sites A and B and make local vlans in site C, so I think I have to have L2 link. I expect 10 hosts + 3 IPPhones in each site. I will be controlling hosts in Site A, B.

[brunop]

Will you then have one vlan for PCs and one for phones?

With so few devices you are probably fine with one flat vlan for all the devices (<30) at sites A & B. I guess my question really is: do you really need to have multiple vlans at A & B if you are planning on trunking them across the sites anyway? The spanning-tree affects will probably be the same.