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Community Member

Multihoming with 2 ISPs: general questions

Greetings!

My company is providing IT services (internet service, WiFi, IPTV, ...etc) to hotels. More and more of our clients ask us about this Multi-homing ISP redundancy solution. I am building a test enviroment and I have found 2 ISPs and I will try this out.

I just want to know how it works between two ISPs. So my router, which has two connections to two different ISPs, will advertise my IP block to them through BGP. I will configure my router (1841) to only accept default route. So for the outgoing traffic, my router should be able to evenly distribute traffics on these two ISPs. However what about incoming traffic? Will they always take the primary link or they can be evenly distributed as well?

Another question is regarding to the AS. The primary ISP asked me to apply for an AS number and they told us that we can use this AS number for other hotels (we have hotels all over in North America and they will very likely use different ISPs). Can we use the same AS number for different hotels in different states or even countries? We don't own any public IP blocks. We will need get individual IP block from each primary ISP for each hotel. Will this cause any problems or we need to apply for individual AS for each hotel?

Thank

9 REPLIES

Re: Multihoming with 2 ISPs: general questions

Greetings!

My company is providing IT services (internet service, WiFi, IPTV, ...etc) to hotels. More and more of our clients ask us about this Multi-homing ISP redundancy solution. I am building a test enviroment and I have found 2 ISPs and I will try this out.

I just want to know how it works between two ISPs. So my router, which has two connections to two different ISPs, will advertise my IP block to them through BGP. I will configure my router (1841) to only accept default route. So for the outgoing traffic, my router should be able to evenly distribute traffics on these two ISPs. However what about incoming traffic? Will they always take the primary link or they can be evenly distributed as well?

Another question is regarding to the AS. The primary ISP asked me to apply for an AS number and they told us that we can use this AS number for other hotels (we have hotels all over in North America and they will very likely use different ISPs). Can we use the same AS number for different hotels in different states or even countries? We don't own any public IP blocks. We will need get individual IP block from each primary ISP for each hotel. Will this cause any problems or we need to apply for individual AS for each hotel?

Thank

Hi,

Check out the belowlink for BGP multihoming configuration in network hope that helps

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a008009456d.shtml

Ganesh.H

Community Member

Re: Multihoming with 2 ISPs: general questions

Thank you for the link Ganesh! I did find that link earlier. I will configure my router the same way. However I am wondering if I can use the same AS number for different sites which use different ISPs. Will that cause problems? I also want to know if there is a way to load balance the incoming traffic? Thanks!

Hall of Fame Super Silver

Re: Multihoming with 2 ISPs: general questions

Hello Zhaodifan,

the key question is :

are your sites inteconnected in some other way, or you would like to use these internet connections also for inter-site communications?

BGP provides a basic loop prevention rule that prevents a BGP router to learn a BGP route with an AS Path attribute containing its own AS.

neighbor ISP-address allowas-in N

allows to override this rule and makes possible to learn routes where the AS path contains up to N times the router BGP AS number

There also some practical limitations that make not possible to advertise prefixes more specific then /24 over the public internet

Edit:

reading your original post leads to think you need to get public ip addresses from different ISPs and that multi-homing  is probably limited to head quarters.

Hope to help

Giuseppe

Community Member

Re: Multihoming with 2 ISPs: general questions

Hey Giuseppe, thank you for reply!

There won't be inter-site traffics. All the hotels are independent. All the traffics are going to internet or from internet (hotel guests are all over the world...)

However it's possible that one hotel guest at this hotel wants to check another hotel's webpage!!!

So there won't be a headquarter (or you can say each hotel is a headquarter themselves!). I will let the router at each hotel learn only the default route from the ISPs so I shouldn't have routes missed in my routing table, I guess?

My concern is that, let's say one hotel in CA is using ISP A&B and its IP range is 1.1.1.0/24. Another hotel in NYC is using another two ISPs C&D and the IP range is 2.2.2.0/24. However they all use the same AS number, let's say 99999. Will C&D learn 1.1.1.0/24 at all because they have already learned 2.2.2.0/24 from the same AS already?? Thanks!

Hall of Fame Super Silver

Re: Multihoming with 2 ISPs: general questions

Hello Zhaodifan,

I remember that strange multicast flooding problem (I hope I'm correct forgive me if it wasn't your issue)

>> Will C&D learn 1.1.1.0/24 at all because they have already learned 2.2.2.0/24 from the same AS already??

this is not a problem for provider routers, but this requires that you apply with ARIN for both /24 IP subnets that will be associated to your public AS number.

As numbers can become easier to get for the introduction of 4 bytes AS numbers, the only IP addresses easy to get are IPv6 addresses.

taking a single /24 and splitting it in two /25 is not allowed by providers.

Hope to help

Giuseppe

Community Member

Re: Multihoming with 2 ISPs: general questions

Hey man,

Yes that weird multicast issue was my problem! I thought I posted in the routing&switching section! Man you are everywhere!

I eventually got the hotel fixed the spanning-tree problem and the multicast was back to normal... Thank you for your help on this one!

So I can use the same AS number for different hotels using different ISPs. However I won't be able to know the other /24 blocks for other hotels. For now I am just applying an AS for my lab. In the future if there are other hotels who want this setup, can I then request /24 from ISP and register their /24 block to this AS number?

Sorry for these many concerns! I think I will stop asking the other questions and get lab setup first and start from there!

Thank you for being interested in my posts!

Difan

Re: Multihoming with 2 ISPs: general questions

Thank you for the link Ganesh! I did find that link earlier. I will
configure my router the same way. However I am wondering if I can use
the same AS number for different sites which use different ISPs. Will
that cause problems? I also want to know if there is a way to load
balance the incoming traffic? Thanks!

Hi,

If your are using public AS number then your AS number should be unique value and if your using a private AS Number then you can use by issuing AS overrite in in other routers.

for incoming traffic check out the MED attribute to enter into your network and check out the below link for more further information hope that help !!

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml

Remember to rate the helpful post !!

Ganesh.H

Community Member

Re: Multihoming with 2 ISPs: general questions

Hey Ganesh,

I finally finished reading the link you gave me as well as some other basic BGP fundamentals and it's very helpful! I will get my lab setup asap and start playing with it. Thank you for the help!

Difan

Community Member

Re: Multihoming with 2 ISPs: general questions

HI,

"I just want to know how it works between two ISPs. So my router, which 
has two connections to two different ISPs, will advertise my IP block to
 them through BGP. I will configure my router (1841) to only accept default 
route. So for the outgoing traffic, my router should be able to evenly 
distribute traffics on these two ISPs. However what about incoming 
traffic? Will they always take the primary link or they can be evenly 
distributed as well?"

Some of the issues in this situation :

will advertise my IP block to
 them through BGP

If you have portable block (The block you received via Regional Registry ) then  only you can advertise the BGP prefix through both ISPs. Otherwise you can advertise the prefix the ISP provided.

my router should be able to evenly 
distribute traffics on these two ISPs

Please Make sure connection based load sharing otherwise you will be end up in problem. Since ISP A never accept traffic that contain ISP Bs ip address.

However what about incoming 
traffic


You can design your network to utilize both ip address ranges . Since the incoming traffic ( eg : web) based on the outgoing traffic ( requests)  so if you do the nat for different ranges for different ISPs load will be balanced.

I had similar issues we solved via natting since we couldn't advertise customer prefix via both ISPs (ISP dependent block) If you have ISP independent no problem

Sorry if i repeat the stuff again .

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