08-24-2011 04:57 AM - edited 03-04-2019 01:23 PM
HI all,
I have 2 * 1Mb ISP link, How can achieve load balancing with redundancy in OSPF.
PLs help..
Thanks in advance
Regards,
Ajith
Solved! Go to Solution.
08-24-2011 05:50 AM
just make sure the iterfaces cost the same
int fa0/1
ip add 1.1.1.1 255.255.255.0
ip ospf cost 10
int fa1/1
ip add 2.2.2.2 255.255.255.0
ip ospf cost 10
router ospf 1
network 1.1.1.1 0.0.0.0 area 0
network 2.2.2.2 0.0.0.0 area 0
smae idea from the other end in adidtion to LAN interface to be advertised in the same area ( both WAN interface has to be same cost and same area )
make sure CEF enabled
ip cef
do not enable per-packet load balncing as advised above as it has some issues with some applications and CPU load
the default per session loadbalancing
this is assumig you are using a leased lines or L2 service provider links
if its L3 such as MPLS you will need to aligne the ocnfig with the SP config but still the concept mentioned required from your end
HTH
if helpful Rate
08-24-2011 05:02 AM
ospf uses costs per link
make sure you have both links using same OSPF cost and the route has be same cost and subnet length
then it will will be installed in you routing table as two next hops
HTH
08-24-2011 05:15 AM
If I am giving the same cost if first link goes down whether the second link will take care all the traffic?Can you share me a sample config..
08-24-2011 05:27 AM
Dear
router ospf XYZ
network x.x.x.x 0.0.0.0 (ip of first p2p link) area X
network y.y.y.y 0.0.0.0 (IP of second p2p link) area X
router-id m.m.m.m (loopback IP) and make sure the ISP also uses their loopback IP as the router ID; the concept s that the next-hop should be an IP equally reeachable via the two links.
maximum-paths 4 (or more)
int Sex/x
ip load-shaering per-packet
(on both p2p int)
and definately if one link goes down all traffic shifts to the other link
08-24-2011 05:50 AM
just make sure the iterfaces cost the same
int fa0/1
ip add 1.1.1.1 255.255.255.0
ip ospf cost 10
int fa1/1
ip add 2.2.2.2 255.255.255.0
ip ospf cost 10
router ospf 1
network 1.1.1.1 0.0.0.0 area 0
network 2.2.2.2 0.0.0.0 area 0
smae idea from the other end in adidtion to LAN interface to be advertised in the same area ( both WAN interface has to be same cost and same area )
make sure CEF enabled
ip cef
do not enable per-packet load balncing as advised above as it has some issues with some applications and CPU load
the default per session loadbalancing
this is assumig you are using a leased lines or L2 service provider links
if its L3 such as MPLS you will need to aligne the ocnfig with the SP config but still the concept mentioned required from your end
HTH
if helpful Rate
08-24-2011 12:22 PM
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To add a bit to what the other posters have already noted, OSPF only supports equal cost load balancing. When you have multiple paths, end-to-end OSPF cost must be the same for multiple entries to appear in the route table.
On Cisco L3 devices, by default, Cisco computes OSPF cost by dividing 100 Mbps by what it believes interface bandwidth to be (can be adjusted by using bandwidth statement). OSPF cost can also be explicitly set on the interface.
Usually, Cisco routers will round-robin flows across the equal cost paths, i.e. at any one time different paths can show very different loads. (NB: PIRO version of PfR can dynamically load balance multiple flows.)
If one path equal path is lost, traffic will immediately use remaining path(s). (NB: immediately isn't actually zero time, but often very, very fast [faction of a second]. This is also after path is detected as being lost, which depending on topology and OSPF settings, can take a while [lots and lots of seconds].)
When multiple paths are available, usually a single flow will only use one path. Load balancing can also be done per packet, but generally not recommended.
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