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Notable Replies

  1. Rene,
    Great lesson however, I have questions if we have two ISPs and we would like to route traffic out through ISP-1. It means we need to set up a higher weight on the ISP-1 peering with us and setup a lower weight on the second ISP-2?
    How can we make sure traffic goes out ISP-1 and comes back in using ISP-2?
    Thanks

    Hamood

  2. Hi Hamood,

    That's right, you can use weight to select the path but this is only for the local router. If you want to influence your entire AS then you'll have to use local preference:

    https://networklessons.com/bgp/how-to-configure-bgp-local-preference-attribute/

    To influence how traffic enters our AS we have a couple of methods, the first one is MED:

    https://networklessons.com/bgp/how-to-configure-bgp-med-attribute/

    This is only useful when you are multihomed to a single ISP. These two methods will help if you are multihomed to different ISPs:

    https://networklessons.com/bgp/how-to-configure-bgp-as-path-prepending/

    https://networklessons.com/bgp/bgp-communities-explained/

    Hope this helps!

    Rene

  3. Hi Rene,
    I have seen some articles regarding to how bgp attributes influence the traffic. There is a table for summary.
    For influence the traffic out of the AS we use local preference inbound, is it possible for you to summary which attribute should be inbound and which should be outbound?
    I assume the table should be like this? Correct me if I am wrong
    attribute inbound(config) influencetraffic
    local preference inbound outbound
    Med outbound inbound
    As prepend outbound inbound
    and so on

  4. Hi Jie,

    Let me give you an overview:


    • Local preference: is propagated throughout the local AS so typically used inbound when we receive eBGP prefixes.

    • MED: sent to neighbor ASes so used outbound.

    • AS Path prepend: normally sent to neighbor ASes so used outbound.

    Rene

  5. Hi William,

    Weight is the first attribute that is used to determine the best path. Here's a nice way to remember the attributes, something I found on a blog a long time ago:

    “We Love Oranges AS Oranges Mean Pure Refreshment”

    W Weight (Highest)
    L LOCAL_PREF (Highest)
    O Originate (local) routes that are advertise through the "network" command or redistributed from an IGP.
    AS AS_PATH (shortest)
    O ORIGIN Code (IGP > EGP > Incomplete)
    M MED (lowest)
    P Paths (External > Internal)
    R RID (lowest)

    Rene

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