I have two links from two different providers. Assuming I have /24 to advertise these two networks which is a min requirement, I'll receive a default routes from them not to consume too much resources and I need to control policies in my local routers. I would prefer a shortest-path for my inbound traffic and/or load-share my links as close as possible... what is the best way for outbound traffic to even out the links if possible? or maybe inbound traffic as well?
under the hyphotesis you own two public /24 address blocks and your own BGP public AS number you are in the conditions of taking advantage of eBGP multihoming.
Towards ISP1 you can send prefix 1 without any prepending and prefix2 with some AS path prepending of your own AS number.
doing the opposite towards ISP2 makes ISP1 the preferred return path for Prefix1 and ISP2 the preferred return path for Prefix2.
Two different route-maps to be applied outbond to neighbors have to be used
This however, can have limited effects because a better connectivity on ISP1 towards some destinations may compensate for your AS path prepending on Prefix2.
The same can happen for ISP2 when looking at Prefix1.
If the two prefixes are also contiguous like 220.127.116.11 and 18.104.22.168 playing on usage of a /23 and sending of only one /24 (prefix1) to ISP1 and sending of /23 and prefix2 to ISP2 can be used.
for outbound traffic if you only receives default routes there is little you can do, just the use of internal routing protocols on internal lan interfaces or of GLBP or MHSRP if blocks apply to client vlans.
the two border routers can publish a default route in OSPF or EIGRP with same parameters devices in internal vlan (to be noted ASA can support this) can install two default routes and can perform per flow load balancing.
The route has to be published only if the BGP 0.0.0.0 is received on the border router and from the eBGP neighbor.
if an iBGP session is used between the two border routers the presence of the route and the route next-hop should be checked.
We have done this successfully with OSPF using
router ospf 10
default-information originate route-map check_BGP type 1
access-list 11 permit host eBGP-next-hopaddress
ip prefix-list only-default permit 0.0.0.0/0
route-map check_BGP permit 10
match ip address prefix only-default
match ip next-hop 11
set metric 50
border routers learn of public address blocks from their IGP neighbors or they perform NAT also
Thanks for a reply...but I have a single public /24 block only. Yes, I own ASN. I understand your scenario below with two prefixes using AS prepending for outbound traffic, one prefix to ASN1 and other prefix to ASN2.
>> In your case, does you links are equally even or close to equal on both incoming and outgoing traffics?
no this is not possible you can achieve usage of both links on both directions
>> For outbound traffic, prefix1 is destined via ISP1 and prefix2 is destined via ISP2 with AS prepending?
no, AS path prepending tries to influence return path not outgoing path there is no attempt to enforce symmetric paths (not required) that would require to use PBR on both routers but it is not needed in usual scenarios
outbound is simply load balancing over two default routes if specific routes are not received from ISP1 and ISP2
>> what if the link is saturated? would there be a possibility to reroute traffic to other link?
this is not possible with BGP alone, for outbound direction without receiving full internet BGP tables you cannot decide out what ISP to go.
to be correct some modern tecniques like OER/PfR can help in detecting that a link is used too much.
>> I am interested of getting the links equal or close to equal use if possible ...
it is simply not possible specially for the return path it is a good result to get both links used in both directions or at least fair outbound load balancing and one link used for return traffic.
This is actually a pretty cool feature, i didn't even know it existed until I was looking for a solution to advertise a subnet (prefix in BGP talk), only if a certain condition existed. This is exactly what conditional advertisements does
j ai une question j ai achete un routeur cisco 887VA-k9 , je le configuré avec la configuration ci- dessous
si je le lier avec mon pc portable sur l un de ses ports directement ça marche toute est bien ( la connexion internet + m...
Attached policy provides CLI access to the Cisco 4G router over text messaging. Two files are in the attached .tar file:
2. PDF with instructions on how to load and use the .tcl file.