From: Petr Lapukhov (petr@internetworkexpert.com)
Date: Fri Sep 19 2008 - 16:44:09 ART
Hi,
"ip tcp ecn" enables ECN support in IOS TCP/IP stack. It has nothing to do
with transit traffic, just with the TCP connections originated/terminated at
router itself. For example it has effect on telnet/HTTP connections to/from
a router. If you want to signal the state of congestion using ECN bits in
the TOS byte, you have to enable WRED with ECN option on interface, to
affect the packets transiting the router.
-- Petr Lapukhov, CCIE #16379 (R&S/Security/SP/Voice) petr@internetworkexpert.comInternetwork Expert, Inc. http://www.InternetworkExpert.com Toll Free: 877-224-8987 Outside US: 775-826-4344
2008/9/19 GAURAV MADAN <gauravmadan1177@gmail.com>
> Hi Petr > > Continuing with that .... can you please tell what task " ip tcp ecn > " perform at the end devices . > > I guess this is more to do with the device in middle informing the end > devices abt the congestion . Can you please tell more abt usage of > this ? > > Thnx > Gaurav Madan > > On Fri, Sep 19, 2008 at 11:08 PM, Petr Lapukhov > <petr@internetworkexpert.com> wrote: > > Igor, > > Those are actually "different" ECN technologies. The first one > > ("random-detect ECN") works with TCP and WRED. Instead of randomly > dropping > > packets, scheduler sets ECN bits in IP header ToS byte, signaling > > ECN-capable endpoints to respond to network congestion. This feature > works > > specifically with TCP and congesting management based on WRED. > > > > The last two have to deal with Frame-Relay ECN signaling. Those are used > in > > Frame-Relay switching code and apply to switched PVCs crossing a > particular > > DCE interface. > > > > The command "frame-relay congestion-management threshold ecn {bc|be} > > <THRESHOLD%>" instructs router to monitor interface output queue. If the > > queue depth grows above the configured "ECN Be" threshold percentage, > then > > the router sets BECN/FECN bits in all input/output Frame-Relay packets > > marked with DE bit. However, if the queue depth climbs above "ECN Bc" > > threshold, then the router adds ECN bits to ALL packets (either DE and > > non-DE marked). Note that this feature is "interface-wide" and affects > all > > PVCs. > > > > You may also enable ECN thresholding on PVC shaping queue, by applying > the > > command "frame-relay congestion threshold ecn" under a "map-class > > frame-relay" for a specific PVC. This feature monitor the specific PVC > > software queue, not the shared interface queue. The procedure makes ECN > > marking "PVC specific" and aware of "per-VC" congestion state. > > > > In addition to ECN signaling thresholds in Frame-Relay networks, you may > > also configure "DE-bit" threshold that specifies the level of queue depth > > where router starts dropping DE-marked packets. > > > > All the above mentioned features are part of Frame-Relay adaptive > congestion > > management. Generally speaking, those are SP related, and you dont have > to > > deal with them in the R&S lab. > > > > HTH > > > > Further Reading: > > > http://www.cisco.com/en/US/docs/ios/wan/configuration/guide/wan_cfg_frm_rly_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1055798 > > > > -- > > Petr Lapukhov, CCIE #16379 (R&S/Security/SP/Voice) > > petr@internetworkexpert.com > > > > Internetwork Expert, Inc. > > http://www.InternetworkExpert.com > > Toll Free: 877-224-8987 > > Outside US: 775-826-4344 > > > > 2008/9/18 Igor M. <imanassypov@rogers.com> > > > >> Hi gang, > >> > >> Anyone knows if there is a significant difference between following fr > >> congestion management tools? > >> > >> 1. under policy-map 'random-detect ecn' > >> 2. under pvc 'frame-relay congestion-management threshold ecn 75' > >> 3. under fr map-class 'frame-relay congestion threshold ecn 75' > >> > >> From what I understand, 2 & 3 would be legacy and 1 comes from MQC. But > >> functionally-wise - are they same or different? > >> > >> Thanks > >> > >> ---------------------- > >> > >> I.M., M.Eng. P.Eng. > >> > >> Network Architect > >> > >> CI Investments > >> > >> ---------------------- > >> > >> > >> Blogs and organic groups at http://www.ccie.net > >> > >> _______________________________________________________________________ > >> Subscription information may be found at: > >> http://www.groupstudy.com/list/CCIELab.html > > > > > > Blogs and organic groups at http://www.ccie.net > > > > _______________________________________________________________________ > > Subscription information may be found at: > > http://www.groupstudy.com/list/CCIELab.html > > > Blogs and organic groups at http://www.ccie.net > > _______________________________________________________________________ > Subscription information may be found at: > http://www.groupstudy.com/list/CCIELab.html
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