03-23-2009 09:00 AM - edited 03-04-2019 04:03 AM
Hi,
We have two sites LAX and SUV with LAX connecting to ISP A and SUV connecting to ISP A and B. We have two identical Cat-4506 (Cisco 4506
CPU at 800Mhz, Supervisor V-10GE/512 Mb)
on both the sites.
Existing Setup:
Site LAX publishes Network A.A.A.A via ISP A
Site SUV publishes Network C.C.C.C via ISP A and with AS path prepend via B with floating static route for fail over.
No Routes learned via any ISP at present.
We have recently setup the 1G link between the sites and hence we would like to use SUV's ISP A and B as fall back for LAX. Also the following conditions have to be met:
1. Network A.A.A.A will only use the ISPA in LAX when the link is functional likewise the site SUV with Network C.C.C.C via ISP A.
2. In the event of a Link Failure in LAX the ISP A in the SUV should be preferred before ISP B.
Given the Hardware Spec(CPU and Memory limitations) please propose a method to achieve all this.
Any Input is greatly appreciated.
Thanks in advance
subra4u
03-23-2009 10:05 AM
(Assuming both LAX and SUV have at least one public AS [yours] and networks A.A.A.A and C.C.C.C are also public [and yours].)
On LAX add another default route to SUV but with a higher cost. If default fails from LAX to ISP-A, outbound traffic should be forwarded to SUV.
Also on LAX, send network A.A.A.A to SUV.
On SUV, pass along network A.A.A.A to both ISPs as you now do with network C.C.C.C but with one or more extra AS prepend hops. (Depending on how LAX and SUV peer, there might already be an extra AS hop.)
03-23-2009 10:19 AM
Hi Joseph,
Thanks for your quick response. We have the same AS for both the Networks A.A.A.A and C.C.C.C. In this Case, I will have to do a iBGP peer between LAX and SUV and in SUV AS prepend will do or should i change the MED values. Please advice.
A quick Is the Hardware good enough to hold a full BGP table.
Thanks in Advance
subra4u
03-23-2009 12:33 PM
Subra:
You cannot use the MED to influence incoming traffic when you are peering with 2 differet AS numbers - 2 different ISPs. So, AS-path prepend is the way to go.
So, I would:
At LAX:
1. Advertise a.a.a.a to ISP A.
2. Advertise c.c.c.c to ISP A with the AS-path prepended.
3. Configure a default route pointing to ISP A and redistiribute it back to your core.
At SUV:
1. Advertise c.c.c.c to ISP A.
2. Advertise a.a.a.a to ISP A with the AS-path prepended.
3. Advertise a.a.a.a and c.c.c.c to ISP B with the AS-path prepended to a length greater than it was for ISP A.
4. Configure a default route pointing to ISP A with an AD of 220 and redistribute that back to your core.
5. Configure a default route pointing to ISP B with an AD of 240 and redistribute that back to your core.
HTH
Victor
03-27-2009 05:21 PM
Hi,
Thanks for your time. I was thinking, if we could influence traffic using MED so that initial failover happens between the same ISP A (incase of a link failure) and use ISP B only as a backup if ISP A is down for some reason. This is mainly because of the commercials involved as we have to pay them(ISP B) based on the utilization. It is just a thought correct me if i am wrong.
cheers
subra
04-06-2009 01:42 AM
Hi All,
I am thinking of having the following config. and try. Please give some inputs on this
On SUV
-----------
router bgp 65535
no synchronization
bgp log-neighbor-changes
network c.c.c.c
network a.a.a.a
neighbor ISP A remote-as 65000
neighbor ISP A soft-reconfiguration inbound
neighbor ISP A distribute-list 3 in
neighbor ISP A route-map setMED-ISPA out
neighbor ISP B remote-as 65001
neighbor ISP B distribute-list 3 in
neighbor ISP B route-map prepend out
no auto-summary
access-list 1 permit a.a.a.a
access-list 2 permit c.c.c.c
access-list 3 permit 0.0.0.0
access-list 3 deny any
route-map setMED-ISPA permit 10
match ip address 1
set metric 200
route-map setMED-ISPA permit 20
match ip address 2
set metric 100
route-map prepend permit 10
set as-path prepend 65535 65535 65535
On LAX
---------
router bgp 65535
no synchronization
bgp log-neighbor-changes
network a.a.a.a
network c.c.c.c
neighbor ISP A remote-as 65000
neighbor ISP A distribute-list 30 in
neighbor ISP A route-map setMED-ISPA out
no auto-summary
access-list 1 permit a.a.a.a
access-list 2 permit c.c.c.c
route-map setMED-ISPA permit 10
match ip address 1
set metric 100
route-map setMED-ISPA permit 20
match ip address 2
set metric 200
thanks
subra
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