Cisco 7200 PCI Limitations

Holmes,David A dholmes at mwdh2o.com
Mon Aug 6 19:55:18 CDT 2012


For users with private DS3-based network links between sites, for the case where 2 or more of these DS3's are to be bundled together in a multi-link PPP connection, Cisco will not support this configuration due to insufficient 7200 cpu resources, so packet-by-packet load sharing must be used which could result in packets arriving out of sequence. Cisco will not support VoIP over packet-by-packet load sharing. Additionally, PIM multicast uses only a single DS3 under the packet-by-packet load sharing scenario, so all available bandwidth with 2 or more DS3s is not available.
The 7200 will support 8 T1s in a logical multilink bundle, though, so for low speed circuits, the 7200 still provides complete IOS feature functionality.
The 7200s have some very limited uses, but in my view they have no place in today's wire speed backbone networks, particularly when 3 or more 7200 GiGE interfaces can be used as a logical bundle. The biggest problem is the tendency of some to treat the 7200 as an Ethernet switch, define a portchannel with 2 or more GiGE interfaces, connect the 7200 portchannel to a modern Ethernet switch, and by this action define a network bottleneck where packets can be dropped due to a serious backplane/wire speed mismatch.

-----Original Message-----
From: PC [mailto:paul4004 at gmail.com]
Sent: Monday, August 06, 2012 10:05 AM
To: david peahi
Cc: nanog at nanog.org
Subject: Re: Cisco 7200 PCI Limitations

While I agree it may not be suitable for transit GigE purposes, it is
certainly acceptable for many WAN aggregation scenarios and CPE scenarios
well in excess of T1 speeds.

There are still many out there in DS3, Fast-E, subrate ethernet subscriber,
ATM, (DSL/L2TP/PPPOE), DMVPN, and other similar scenarios.  For this, while
often not ideal, they continue to work fine.

On Mon, Aug 6, 2012 at 10:47 AM, david peahi <davidpeahi at gmail.com> wrote:

> The 7200 architecture dates from the late 1990s, and is basically modeled
> on a PCI-bus UNIX workstation from that era. The 7200 is usable today as a
> WAN aggregation router for T1 access, and nothing else. Using it as a GiGE
> transit router will place a non-deterministic node in the network, unable
> to scale to the 4 GiGE full-duplex throughput. Even worse is creating a
> portchannel out of the 7200 GiGE interfaces and using dot1q sub-interfaces
> to emulate an Ethernet switch in 7200 software, then connecting the 7200
> dot1q trunk to a modern Ethernet switch with a wire speed backplane (for
> example a Cisco 3560X Ethernet switch).
> Long since considered an unacceptable best practice (due to the 7200
> backplane limitation vs adjacent, directly connected modern Ethernet
> switches), Cisco is still teaching portchannel in its router configuration
> classes, so relatively new network engineers have actually been known to
> use this ill-considered configuration.
> If a 4 port GiGE Cisco router is needed, then the ASR1001 is the modern
> version of the 7206, with wire speed throughput.
>
> On Fri, Aug 3, 2012 at 12:36 AM, shthead <lists at shthead.com> wrote:
>
> > Hi all,
> >
> > I have a 7200 series router (7204) here and I am trying to figure out
> > something with it. Currently the router has a NPE-G1 card in it, giving
> it
> > 3 gig interfaces but I need an extra gig interface on it to make 4.
> >
> > Having a look around the available options are either get a PA-GE card
> > that fits into one of the slots on the router or to get a C7200-I/O-GE+E
> > (I/O controller with a gbit port on it).
> >
> > The PA-GE wouldn't be suitable as looking at the Cisco site the PCI bus
> > will limit it to 300mbit full duplex (and it goes on further to say it
> will
> > be limited to approx 200mbit in best case scenario due to the design of
> the
> > card) [1].
> >
> > The other option left is the I/O controller. I found that you can get a
> > port adaptor jacket card [2] for the 7200's that let you stick a normal
> > interface card into the I/O controller slot (instead of the I/O
> controller
> > itself).
> >
> > My main concern is if the jacket card uses its own PCI bus I am assuming
> > the C7200-I/O-GE+E also connects via PCI which means it would be subject
> to
> > the same limitations as the PA-GE.
> >
> > Does anyone have any idea if that would be correct and the only option
> for
> > another gbit port would be to get another device?
> >
> > Thanks for the help
> >
> > [1] http://www.cisco.com/en/US/**products/hw/routers/ps341/**
> > products_tech_**note09186a00800c814a.shtml#**backinfo<
> http://www.cisco.com/en/US/products/hw/routers/ps341/products_tech_note09186a00800c814a.shtml#backinfo
> >
> > [2] http://www.cisco.com/en/US/**prod/collateral/routers/ps341/**
> > prod_qas0900aecd8045055e.html<
> http://www.cisco.com/en/US/prod/collateral/routers/ps341/prod_qas0900aecd8045055e.html
> >
> >
> >
>

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