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Forum Replies

  1. My company have two ISP connections but we only use 1 for all our traffic and the other was is for backup situation. We were planning to buy a netgear router (http://www.netgear.com.au/business/products/security/FVS336G.aspx#tab-features). There are two WAN port and it has load sharing capability. Are you saying that in the configuration we will not be able to set 80% to ISP 1 and 20% to ISP2 and it will be 50/50 distribution only? and if we do want to send 80% trafic through 1 ISP and 20% through another we don’t have an other option but to buy beefy routers to run BGP. Moreover, I heard that bgp is more about controlling incoming traffic flow from multiple ISPs to your network (you may be running multiple webserver in your network)rather than outgoing traffic from your network?

  2. Hi Lorenzo,

    Thanks, glad to hear you like it!

    That capture looks weird…I haven’t seen it before and I can’t find anything about it. Where did you find it?

    Seeing multiple update messages in one frame is normal but I haven’t seen open + keepalive combined. Here’s a wireshark capture I just did on two IOS 15 routers with external BGP:




  3. Hi Lorenzo,

    I took a look, with google translate I can get pretty far :slight_smile:

    About the update message…

    • When the path attributes for prefixes are the same then BGP will combine them in a single update message.
    • When the path attributes for prefixes are different then BGP will use multiple updates messages but they can be in the same frame.

    Take a look at these two wireshark captures. In the first one the path attributes are the same and in the second one they are different.

    BGP same path attributes

    BGP different path attributes

    Hope this helps.


  4. andrew says:

    I think you are asking two questions:

    1. unless you are assigned an ASN by an Internet authority, like ARIN, then it is common practice for ISPs to use a private BGP AS when they peer with you. These AS numbers are not allowed on the Internet, so the ISP will translate them into their own AS number before routes leave their AS to another ISP or organization. Think of it like BGP “NAT” where inside the ISP a private range is used, and gets translated to a publicly recognized range. Because of this, the customer will not have any problems with loop prevention with BGP

    2. It is also possible (and common) for ISPs to use the same private AS number among many of their customers. They can get away with this by use VRFs (virtual routing and forwarding). The setup of this feature can get a little complex because you have to use things called Route Distinguishers and Route Targets (both import and export). Here is a link where Cisco talks about how BGP works with VRF

  5. Great lesson so far its simple and straight forward. I have read further in the book though and I will have questions but first trying to catch up on the web pages to see if that helps push some ideas that I stalled a little bit on. Its more along the lines of using Internal with external and some differences with BGP not seeing networks like the others. I don’t want to ask that question here though as I want to put the question under the right lesson if I still have confusion after reading.

    great stuff!

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