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I have a cisco2821 router and it has connected to one Internet service provider. Now i need to buy another one router so that i can have another Internet provider which can help me when one primary Internet fails another one helps. So now i need to do Multi homing Border gateway protocol in both the routers but some are saying that we cannot do border gateway protocol in in cisco2821 router?

Can we do border gateway protocol in cisco2821 router? And also i need to know whether cisco890 series routers are dual wan routers?

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  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin ♦
    Apr 1 '18 at 22:27
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Yes, the Cisco 2821 can run BGP. What you need to clarify is the level of BGP advertisements. Are you receiving the full Internet routing table? If so, you probably8 need a router with more resources.

When you ask about dual WAN routers, understand that your routers have no idea what is WAN or LAN. The routers route between networks, and any or all of the networks could be WAN or LAN (however you define that).

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  • can you please suggest me a router through which i can use multiple isp
    – Travis cook
    Mar 14 '18 at 13:05
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    Product or resource recommendations are explicitly off-topic on SE sites, except Software Recommendations and Hardware Recommendations. Either of the routers you mention can be used with multiple ISPs.
    – Ron Maupin ♦
    Mar 14 '18 at 13:07
  • Both can be used for multi-ISP connection, but you should check available memory on them in case if you would like to store 2 or more full-views.
    – Andrey Prokhorov
    Mar 14 '18 at 15:02
  • @Traviscook You can ask your ISP to send you a default route only, in which case your 2821s will work just fine.
    – Ron Trunk
    Mar 14 '18 at 15:28
  • What you need to clarify is the level of BGP advertisements?can you please tel me exactly waht it means coz i'm a rookie
    – Travis cook
    Mar 15 '18 at 12:34
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Yes, a Cisco 2821 can do BGP. But as Ron mentioned, it will have a limited amount of memory available to hold prefixes that BGP learns. If you're trying to use two ISPs for internet multi homing, then there are 3 ways to do it:

  1. Ask your ISPs for a default route: Each router receives a quad-zero route via BGP. Traffic from the internet comes in to both routers, but traffic to the internet uses one provider only. The other router is a backup. This way requires no memory upgrade in a 2821 router, but it's letting a lot of bandwidth go idle. You will have asymetric flows with this method, but it's nothing to worry about.
  2. Ask your ISPs for partial routes plus default: Each router receives the routes that each ISP directly manages, plus a quad-zero route. Traffic from the internet comes in to both routers, and traffic to the internet will use some bandwidth on the second link, but the majority on the first link, depending on how well-connected your two providers are. This way requires no memory upgrade, but you'll need to be careful that you don't cause your routers to reboot if they run out of memory.
  3. Ask you ISPs for full internet routes: Traffic from the internet comes in to both routers, and traffic to the internet uses both routers, but maybe not equally. That's okay, though, because it will be best-path, not half-and-half. Basically, traffic will take the path that is best, not the path that keeps your circuits equal. This way will require a memory upgrade for a 2821 router. If you don't get the memory upgrade, your router will reboot continually, each time it establishes BGP and gets the full internet routing table, and runs out of memory.

Therefore, pick the best redundancy that you can with what you have. Or else, get some newer routers. (Those 2821s are EoL!)

Regarding the 890 router doing dual wan, all modern Cisco routers can handle dual wans, but it depends on what you're trying to do. The 890 will not do WAN load balancing, but it will certainly allow you to connect two WAN circuits (with ethernet handoffs) and use them both based upon dynamic routing, floating statics, or IP SLA. It will not allow you to use one WAN for certain TCP ports and the other WAN for some other TCP ports. That's SDWAN.

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