While several of us have mentioned splitting up the netblocks that you advertise to your ISP would help spread the usage across the T1's there is something to keep in mind. If there is only 1 or so hosts that are most often the destination for traffic inbound to your site, you are still going to get more utilization across the link that advertises the network that contains that particular host/s.
I mention this because I've had clients in the past split netblock assignments in an effort to get better utilization of their multiple T1 setups. But we've often found that they have 1 host providing more service than the others, that particular network will see more traffic, hence, that particular link seeing more utilization. There can be a need to be very granular about how you advertise networks and about how you have your network set up. You may have to play with moving hosts around on different netblocks if you are truly looking to get something near even traffic on each T1. You can use your interface stats to routinely check load, or better, use something like MRTG that will poll your interfaces and graph utilization over longer periods of time. Sorry if this is long winded, but you need to keep in mind what your trying to do. How to best use the resources you have and perhaps most importantly, to know how to measure it accurately to see if you've achieved the results you were looking for. -chris ----- Original Message ----- From: "YASSER ALY" To: Sent: Monday, December 23, 2002 11:43 AM Subject: Re: HSRP and BGP [7:59735] > In your scenario advertising same block over both links to your provider > will not help in load sharing. Redundancy is acheived but not sharing > because your ISP will receive two advertisments to the same block and BGP > only chooses the best route. > > You can overcome this in many ways, for example you if you have a /22 > block. Devide it into 8 /24 blocks. Start advertising 4 /24s through the > 1st router, advertise the remaining /24s through the 2nd router. Like > this you acheived load-balance as your ISP will receive 1/2 of the routes > via one link and the rest through the other. > > You are not done yet as this will provide load-sharing but not > redundancy. For example if Link1 fails this means that 1/2 of your blocks > will not be advertised and will stop receiving traffic for them. To avoid > this, advertise through both routers an aggregate route for the whole > /22. Like this your ISP will always use the more specific route and in a > way balance the traffic over both links. When one of the links/routers > fail, your ISP will use the aggregate route advertised from your other > router to route all the traffic back to you. > > Another way, is to ask your provider to accept not just 1 route for the > /24 but accept both by setting the maximum accepted routes to 2 instead > to 1. 1 is the default and ISPs normally don't accept changing this > default value. > > HTH, > > Yasser > > >From: "Ivan Yip" >Hi All, > >Thanks all your response. > >Now two > routers adverise same block /24 to the isp. I found that they are >'load > shared' in this sense. Only 1 link is the active for Inbound. For > >example, if I download files from outside, inbound is using say link1 > and >link2 is idle and no packet coming in. Some time later, I ftp again > and this >time is using link2 and link1 is idle. > >Is it normal? > >TIA. > misconduct and Nondisclosure violations to [EMAIL PROTECTED] > > ------------------------------------------------------------------------ > > Protect your PC - Click here for McAfee.com VirusScan Online Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=59759&t=59735 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
