Implementing Advanced Services Today – Routing & Multicast

Implementing Advanced Services Today – Routing & Multicast

ken lindahlChair, Internet2 Routing Working [email protected]

Campus Focused Workshop on Advanced NetworkingSan Diego, CA4 December 2000

4 December 2000 2Campus Focused Workshop on Advanced Networking 4 December 2000

Routing

4 December 2000Campus Focused Workshop on Advanced Networking 34 December 2000

Routing Working Group

Chair: ken lindahl, UC Berkeley

current topics:

•Explicit Routing• Internet2 Routing Registry (I2db)• Internet2/Commodity Internet Routing Asymmetry

http://www.internet2.edu/routing/


Internet2 / Commodity Internet Routing Asymmetry

traffic between two Internet2 sites uses Abilene in one direction and commodity Internet in the other.reduced performance: lower bandwidth, greater latency, greater jitter, higher packet loss

reported by Hank Nussbacher at Spring 2000 Members Meeting• http://www.internet-2.org.il/i2-asymmetry/

very pronounced cases can be seen in the Abilene Connector mrtg graphs (Joe St Sauver)

– http://monon.uits.iupui.edu/abilene/


Asymmetry example #1Abilene Connector mrtg graphs

e.g. Georgetown (NYCM Connector) 11/30/2000

http://monon.uits.iupui.edu/abilene/nycm/georgetown-bits.html

in / max in (to Abilene) out / max out (from Abilene)


Asymmetry example #2Abilene Connector mrtg graphs

e.g. Cornell (NYCM Connector) 11/30/2000

http://monon.uits.iupui.edu/abilene/nycm/cornell-bits.html

in / max in (to Abilene) out / max out (from Abilene)


Abilene Connector mrtg graphsLimitations

Abilene Connector mrtg graphs won’t show asymmetry in many cases, e.g.:

campus connects to a gigaPoP• Abilene graphs will show aggregated statistics for all campuses connected to the gigaPoP, tending to hide asymmetry for a single campus.

• gigaPoP and campus graphs might reveal asymmetry.• but, some gigaPoPs offer “shared” ISP; campuses may have a single link to gigaPoP for both Internet2 and commodity traffic.

• campus mrtg graphs won’t reveal asymmetry in this case.


Abilene Connector mrtg graphsLimitations

Abilene Connector mrtg graphs won’t show asymmetry in many cases, e.g.:

parts of the campus network are routed asymmetrically

• incorrect BGP configuration prevents some campus prefixes from being announced

• some campus subnets don’t reach Internet2 connection; instead, follow campus default to commodity Internet.


Asymmetry example #3Asymmetry of Internet-2, slide 17

source: The Asymmetry of Internet2, Hank Nussbacher, March 2000, http://www.internet-2.org.il/i2-asymmetry/



– slide 18 from Hank’s talk



Routing Asymmetry

estimated 30% of Internet2 exhibits this sort of asymmetry

– The Asymmetry of Internet-2, Hank Nussbacher, March 2000

in some cases, campuses are aware of the issue; need to upgrade network equipment to fix.


Detecting Asymmetry


Detecting AsymmetryNussbacher’s Looking Glass test


Detecting Asymmetry

campus Surveyor or NLANR AMP might be able to detect asymmetry

http://www.advanced.org/surveyor/

http://amp.nlanr.net/• typically located near the campus Internet2 link, so might not detect asymmetries affecting interior subnets.

traceroute to Internet2 sites from interior subnets• will reveal instances where outbound data is via the commodity Internet.

• time-intensive.• not available to network engineers at other sites.


Detecting Asymmetry

Abilene Core Node Router Proxy can be used to check campus BGP announcements

• doesn’t really show that data will be delivered correctly• … but if the BGP announcements are incorrect, packets are unlikely to take the desired path.

Summary: several incomplete and/or inadequate tools exist. Routing WG will investigate this issue and try to find a solution.

• participants will be welcomed! to join, see

http://www.internet2.edu/routing/


Interior routing

what’s to say?

encourage use of link-state IGP, e.g. OSPF, EIGRP (cisco proprietary).

generally, not necessary to redistribute external routes into IGP; instead use default to deliver packets to border router, let BGP do the work from there.

most importantly, make sure the packets are following intended paths.


port duplex mis-matches

not routing, per se…

some think this is the most commonly seen performance killer in the Internet today.

often is the result of autonegotiation failure between connected devices.

YMMV, consider disabling autonegotiation; rely on manually configured speed and duplex...

• … especially on switch-to-switch and switch-to-router links (how often do these change speed or duplex?)

4 December 2000 18Campus Focused Workshop on Advanced Networking 4 December 2000

Multicast


Multicast Working Group

Chair: Kevin Almeroth, UC Santa Barbara

currently focused on encouraging campus deployment of IP multicast

http://www.internet2.edu/multicast/

disclaimer: content of this presentation should be blamed on ken, not Kevin.


Internet2 Multicast Architecture

PIM Sparse-Mode• avoids periodic flooding of all multicast groups; important for high-bandwidth Internet2 multicast applications.

MBGP on border routers• allows non-congruent unicast and multicast topologies; important when a site does not use it’s ISP for multicast.

MSDP between neighboring ASs• communicate Sender Active information to RPs in all external PIM domains.

for details, see NCNE Multicast page;• http://www.ncne.org/faq/multicast.html


PIM issues

version: should be PIMv2• vendor interoperability (e.g. Nortel: PIMv2 SM only)• cisco: requires IOS 12.0 or later

auto-RP vs. BootStrap Router (BSR)• auto-RP is cisco-proprietary; supports cisco’s v1/v2 interoperability mode; requires Sparse-Dense-Mode (interior interfaces only); works with administratively scoped zones

• BSR is part of PIMv2 spec, supports vendor interoperability; may not work with administratively scoped zones (still true?)


Monitoring Multicast

NLANR Beacon• loss• one-waydelay

• jitter• out-of-orderarrivals

• duplication

Beacon - The Big Picture

B

B B

B B

BeaconServer

BeaconViewer Web browser

traffic reports

query and reply

multicast probes

(user interface)



NLANR Beacon• documentation and source (java), available at http://dast.nlanr.net/Projects/Beacon/

Abilene Beacon page• http//palpatine.ucs.indiana.edu:9999/• only two sites currently; not ready for prime-time?

suggestion: deploy Beacons around campus to monitor campus multicast; also one at/near border to peer with GigaPoP and other campuses.



Abilene multicast tools• Multicast Route Viewer, MSDP logger, SDR Monitorhttp://www.abilene.iu.edu/index.cgi?page=multicast

SDR Monitor at UCSB• http://steamboat.cs.ucsb.edu/sdr-monitor/• shows whether SDR announcements from your campus are getting out

• also, gives an idea of what SDR announcements your campus should be able see

list of multicast monitoring and debugging toolshttp://www.ncne.nlanr.net/faq/mcast_eng_faq.html#42


Multicast bandwidth control usingrate-limiting

cisco routers support configurable rate-limits on interfaces

ip multicast rate-limit out 4000ip multicast rate-limit in 4000

• limits total {in,out}bound multicast to 4Mbps

when configured limit is exceeded, multicast packets are dropped indiscriminately

• some multicast is pretty important and should not be dropped: OSPF, PIM messages, NTP

• can use access-lists to exempt well-known groups from rate-limiting


Multicast bandwidth control using administratively scoped zones

parts of the campus network that are not able to handle high-bandwidth multicast (e.g. >10Mbps) need protection

if the sender is on your campus and you can influence the group address that is used, administratively scoped multicast boundaries can keep users in bandwidth-challenged parts of the network from joining high-bandwidth sessions.

but you probably can’t control sessions that originate from outside your campus.

configuration can be complicated, involving multiple RPs and multiple RP mapping agents, each carefully scoped.

• c.f. Developing IP Multicast Networks, Beau Williamson, Cisco Press


Constraining multicast flooding –IGMP Snooping vs CGMP

IGMP Snooping• switch inspects IGMP membership reports from hosts to determine which ports a group should be forwarded out

• can be CPU intensive (switch must inspect all multicast packets).

• implementations appear to differ among vendors.

CGMP• switch forwards IGMP membership reports to router; router uses CGMP to tell the switch which ports a group should be forwarded out

• moves CPU load to the router (minimal)• cisco proprietary


Constraining multicast flooding –IGMP Snooping vs CGMP

use one or the other on switched LANs that have connected hosts

Issue: leave latency• IGMPv1 hosts do not send IGMP Leave Group messages, so forwarding state on switch must time out. (Affects both IGMP snooping and CGMP).

Issue: does not work on router ports• routers don’t send host membership reports, so neither IGMP snooping nor CGMP works on router ports. Don’t use either on a backbone switch with only routers attached.


the next thing: SSM

Source-Specific Multicast• addresses scalability issue of earlier forms of multicast• receivers specify desired source when joining group• source and group information learned via non-multicast means (e.g. web page)

requires IGMPv3 for (S,G) joins• some host implementations are available• requires support in last-hop router (cisco EFT images now, supported releases soon)

• cisco offers 2 interim workarounds: IGMPv3lite and URD (URL Rendezvous Directory)


the next thing: SSM

cisco informationhttp://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121newft/121t/121t3/dtssm.htm

U of Oregon SSM trialhttp://videolab.uoregon.edu/projects.html

IETF WGhttp://www.ietf.org/html.charters/ssm-charter.html

Implementing Advanced Services Today – Routing & Multicast

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