some comments on draft-ietf-idr-bgp4-experience-protocol-02.txt
Curtis Villamizar <curtis@laptoy770.fictitious.org> Wed, 17 September 2003 14:44 UTC
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Subject: some comments on draft-ietf-idr-bgp4-experience-protocol-02.txt
Date: Wed, 17 Sep 2003 10:38:08 -0400
From: Curtis Villamizar <curtis@laptoy770.fictitious.org>
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ref: Title : Experience with the BGP-4 Protocol Author(s) : D. McPherson, K. Patel Filename : draft-ietf-idr-bgp4-experience-protocol-02.txt Danny, This looks to be in good shape. If you do another version of the draft here are some suggestions. None of this is essential to the draft but it might be helpful. Curtis In the MED section you might want to describe the common "hot potatoe / cold potatoe" usage. Here is some suggested text. In a situation where traffic flows between a pair of destinations, each connected to two transit networks, each of the transit networks has the choice of either sending the traffic to the closest peering to other transit provider or passing traffic to the peering which advertises the least cost through the other provider. The former method is called "hot potatoe routing" because like a hot potatoe held in bare hands, whoever has it tries to get rid of it quickly. Hot potatoe routing is accomplished by not passing the EGBP learned MED into IBGP. This minimizes transit traffic for the provider routing the traffic. Far less common is "cold potatoe routing" where the transit provider uses their own transit capacity to get the traffic to the point in the adjacent transit provider advertised as being closest to the destination. Cold potatoe routing is accomplished by passing the EBGP learned MED into IBGP. If one transit provider uses hot potatoe routing and another uses cold potatoe, traffic between the two tends to be symetric. Depending on the business relationships, if one provider has more capacity or a significantly less congested transit network, then that provider may use cold potatoe routing. An example of widespread use of cold potatoe routing was the NSF funded NSFNET backbone and NSF funded regional networks in the mid 1990s. In some cases a provider may use hot potatoe routing for some destinations for a given peer AS and cold potatoe routing for others. An example of this is the different treatment of commercial and research traffic in the NSFNET in the mid 1990s. Optionally add to the last paragraph "This might best be described as 'mashed potatoe routing' a term which reflects the complexity of router configurations in use at the time". :-) Under "Internet Dynamics" I would prefer if you would add: None of the current implementations of BGP Route Flap Damping store route history by unique NRLI and AS Path although it is listed as manditory in RFC 2439. A potential result of failure to consider each AS Path separately is an overly aggressive suppression of destinations in a densely meshed network, with the most severe consequence being suppression of a destination after a single failure. Because the top tier AS in the Internet are densely meshed, these adverse consequences are observed. After "Limit Rate Updates" you might add a section: 13 1/2. Consideration of TCP Characteristics If a TCP receiver is processing input more slowly than the sender or if the TCP connection rate is the limiting factor, a form of backpressure is observed by the TCP sending application. When the TCP buffer fills, the sending application will either block on the write or receive an error on the write. Common errors in either early implementations or an occasional naive new implementation are to either set options to block on the write or set options for non-blocking writes and then treat the errors due to a full buffer as fatal. Having recognized that full write buffers are to be expected additional implementation pitfalls exist. The application should not attempt to store the TCP stream within the application itself. If the receiver or the TCP connection is persistently slow, then the buffer can grow until memory is exhausted. A BGP implementation must send changes to all peers for which the TCP connection is not blocked and must remember to send those changes to the remaining peers when the connection becomes unblocked. If the preferred route for a given NLRI changes multiple times while writes to one or more peer is blocked, only the most recent best route needs to be sent. In this way BGP is work conserving. In times of extremely high route change, a higher volume of route change is sent to those peers which are able to process it more quickly and a lower volume of route change is sent to those peers not able to process the changes as quickly. For implentations which handle differing peer capacity to absorb route change well, if the majority of route change is contributed by a subset of unstable NRLI, the only impact on relatively stable NRLI which make an isolated route change is a slower convergence for which convergence time remains bounded regardless of the amount of instability.
- some comments on draft-ietf-idr-bgp4-experience-p… Curtis Villamizar