I'm about to get a dual-T1 solution from a major telco. vendor; a connection to the Internet. They offer per-destination & per-packet options on CEF configuration. Question on per-destination: Let's say I have 100 people with 100 TCP connections open to CNN.COM. Will each of the 100 separate TCP connections go to a different T1, or will the router ensure that ANY traffic destined for CNN.COM goes to a *single* T1?
with per-destination load sharing, your 100 users will get evenly distributed over both T1 links, but the source-destination traffic stream will always stay on the same link. So if one of your users downloads large files, that traffic will not be load-shared over both links, which can lead to, in effect, unbalanced load-sharing.
With per-packet load sharing you can achieve true load-sharing, since the router sends successive data packets over paths without regard to individual hosts or user sessions. It uses the round-robin method to determine which path each packet takes to the destination.
Check out this document for the detailed explanantion from Cisco:
Troubleshooting Load Balancing Over Parallel Links Using Cisco Express Forwarding
CEF by default uses a hash algorithm, which calculates a hash based on source and destination ip address pair. This hash is used to select the route (in your case, default routes to the ISP). So if 100 users are accessing CNN.com, each user will alternate between the T1s.
Like said, in the other post, if one user downloads a large file, you wont be able to share the load between the T1s. So its better that you enable per packet load sharing.
Original Poster here. I'll be doing the dual-T1 config on a 2611XM with one of the K9 IOS's from the 12.1 train I think. Two WIC-T1-DSU cards in it. 2611XM is an 80Mhz CPU(?) I also have a 1751 available as well, which is better?
according to Cisco there is no performance degradation:
Load balancing with CEF for IP
In IOS software 11.1CC a new forwarding mechanism for IP packets was introduced: Cisco Express Forwarding (CEF). The design of Cisco Express Forwarding includes enhancements that allow to use load balancing without sacrificing forwarding performance even when using per packet load balancing. Previously per packet load balancing required disabling of route-caching mechanisms like fast switching or optimum switching (see above paragraph). CEF is available in IOS software version 11.1CC for Cisco 7200 and 7500 series routers only. CEF currently supports the following encapsulations: ATM/AAL5snap, ATM/AAL5mux, ATM/AAL5nlpid, Frame Relay, Ethernet, FDDI, PPP, HDLC, and tunnels.
Question We run asr9001 with XR 6.1.3, and we have a very long delay to
login w/ SSH 1 or 2 to the device compare to IOS device. After
investigation, the there is 1s delay between the client KEXDH_INIT and
the server (XR) KEXDH_REPLY. After debug ssh serv...
Introduction The purpose of this document is to demonstrate the Open
Shortest Path First (OSPF) behavior when the V-bit (Virtual-link bit) is
present in a non-backbone area. The V-bit is signaled in Type-1 LSA only
if the router is the endpoint of one or ...
Hi, I am seeing quite a few issues with patch install and wanted to
share my experience and workaround to this. Login to admin via CLI, then
access root with the “shell” command Issue “df –h” and you’ll probably
see the following directory full or nearly ...