12-02-2009 08:51 AM - edited 03-04-2019 06:51 AM
Hi,
My network is as follows -
1. at Data Center i have one 3750 Switch Stack (2 x 3750 Switches in stack) acting as a L3 Core Switch. It connects to 2 WAN routers cisco 2811.
2. at DR i have only one 3750 Switch, no switch stack. This siwtch connects to 2 WAN routers cisco 2811.
3. both the WAN routers at DC & DR connects to each other using Point-to-Point leased lines. ie., DC_R1 connects to DR_R1 and DC_R2 connects to DR_R2
4. DC Core Switch and WAN Routers are configured with BGP AS 65534. DR Core Switch and WAN Routers are configured with BGP AS 65532. DC Core Switch & DC WAN Routers establish a iBGP session, same in DR. Whereas DC WAN Routers & DR WAN Routers establish eBGP session.
5. It is required by customer to load balance and load share traffic between the 2 x WAN routers, so i need to see 2 x routes in the L3 Core Switch at DC & DR. It is configured under BGP with command "maximum-path ibgp 2". This allows the 2 x learned BGP routes into IP Routing table.
6. In DR Core Switch i see 2 equal cost routes and "multipath" in "show ip bgp x.x.x.x", but where as in DC i do not see "multipath" in show ip bgp. Though there are 2 x equal cost paths from the DC core switch, only one best path is shown in show ip bgp.
7. what is difference between the metric just next to the neighbor from which it is learned the route and the metric 0 below it. please see the show ip bgp output
DC_L3_SW#sh ip bgp 164.53.211.198
BGP routing table entry for 164.53.211.192/27, version 45
Paths: (2 available, best #2, table Default-IP-Routing-Table)
Multipath: iBGP
Advertised to update-groups:
2
65532
10.177.44.186 (metric 2172416) from 10.177.43.70 (10.177.44.185)
Origin IGP, metric 0, localpref 100, valid, internal
65532
10.177.44.178 (metric 1764352) from 10.177.43.66 (10.177.44.177)
Origin IGP, metric 0, localpref 100, valid, internal, best
DR_L3_SW#sh ip bgp 164.53.211.128
BGP routing table entry for 164.53.211.128/27, version 98
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Multipath: iBGP
Advertised to update-groups:
2
65534
10.177.44.177 (metric 2172416) from 10.177.43.74 (10.177.44.178)
Origin IGP, metric 0, localpref 100, valid, internal, multipath, best
65534
10.177.44.185 (metric 2172416) from 10.177.43.78 (10.177.44.186)
Origin IGP, metric 0, localpref 100, valid, internal, multipath
i have verified the cost value (bandwidth) of all the interfaces in path, and they all match. Serial interfaces are configured bandwidth to 2048 kbps on both WAN routers. Fast ethernet links are bandwidth 100mbps.
Please ref to the Network Diagram attached.
Please can any one help on how to solve this problem, DC L3 Core Switch is also required to have 2 x equal cost routes to the DR subnet.
Regards,
Keshava Raju
12-02-2009 09:36 AM
Could you provide -
"sh ip route" from the 3750 switches
config of routers
Jon
12-02-2009 09:38 AM
Hi keshava Raju,
From your output:
10.177.44.178 (metric 1764352) from 10.177.43.66 (10.177.44.177)
Origin IGP, metric 0, localpref 100, valid, internal, best
1764352 represent the IGP metric to the BGP next-hop which is 10.177.44.178 in this case.
metric 0 represent the MED associated to the prefix.
It means that DC_L3_SW had computed a different EIGRP metric to reach 10.177.44.178 and this is what you need to fix as iBGP multipath will take place only if the IGP cost to each BGP next-hop are the same.
EIGRP is using a composite metric so you need to be sure bandwidth and delay are exactly the same on every interface.
HTH
Laurent.
12-02-2009 11:49 PM
Hello Mr. Laurent,
Thanks for your feedback... it really helped.
But the problem still persists.
In India the Point-to-Point leased lines provided by ISP is 2MB (2048 kbps). I have changed the bandwidth on the Serial Interfaces of all the 4 routers to 2048 kb. But still in the routing table, route from the DC_L3 switch to the DR Serial Interface it shows as bandwidth 1544 kb. How can this happen?
Please find the below show ip route & show ip eigrp topology from the DC & DR L3 core switch -
*************************************************************************************************************************************************
DC_L3_SW#sh ip eigrp topology 10.177.44.184/30
EIGRP-IPv4:(999) (AS 999): Topology Default-IP-Routing-Table(0) entry for 10.177.44.184/30
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 1764352
Descriptor Blocks:
10.177.43.70 (Port-channel2), from 10.177.43.70, Send flag is 0x0
Composite metric is (1764352/1761792), Route is Internal
Vector metric:
Minimum bandwidth is 2048 Kbit
Total delay is 20100 microseconds
Reliability is 255/255
Load is 1/255
Minimum MTU is 1500
Hop count is 1
DC_L3_SW#sh ip route 10.177.44.186
Routing entry for 10.177.44.186/32
Known via "eigrp 999", distance 90, metric 2172416, type internal
Redistributing via eigrp 999
Last update from 10.177.43.70 on Port-channel2, 00:33:30 ago
Routing Descriptor Blocks:
* 10.177.43.70, from 10.177.43.70, 00:33:30 ago, via Port-channel2
Route metric is 2172416, traffic share count is 1
Total delay is 20100 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
DC_L3_SW#sh ip eigrp topology 10.177.44.17 6/30
EIGRP-IPv4:(999) (AS 999): Topology Default-IP-Routing-Table(0) entry for 10.177.44.176/30
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 1764352
Descriptor Blocks:
10.177.43.66 (Port-channel1), from 10.177.43.66, Send flag is 0x0
Composite metric is (1764352/1761792), Route is Internal
Vector metric:
Minimum bandwidth is 2048 Kbit
Total delay is 20100 microseconds
Reliability is 255/255
Load is 3/255
Minimum MTU is 1500
Hop count is 1
DC_L3_SW1#sh ip route 10.177.44.178
Routing entry for 10.177.44.176/30
Known via "eigrp 999", distance 90, metric 1764352, type internal
Redistributing via eigrp 999
Last update from 10.177.43.66 on Port-channel1, 00:32:34 ago
Routing Descriptor Blocks:
* 10.177.43.66, from 10.177.43.66, 00:32:34 ago, via Port-channel1
Route metric is 1764352, traffic share count is 1
Total delay is 20100 microseconds, minimum bandwidth is 2048 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 3/255, Hops 1
*******************************************************************************************************************************************************
I have tried clearing ip eigrp neighbors and removing the interfaces and connecting back to the L3 core switch. But still the bandwidth of the neighbor 10.177.44.186 still shows as 1544 kbps, where i have already changed the Bandwidth on the Serial Links to 2048kbps.
Please can help me know how to solve this problem!
Regards,
Keshava Raju
12-03-2009 06:22 AM
Hi,
Did you check the Bw and delay of all port-channel interfaces as well ?
I agree it's not normal. Did you try also a clear ip route * ? Are both core switched running the same version ?
Another option, could be to use bgp next-hop-self feature on your eBGP routers toward your core switch.
Thanks
Laurent.
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