Re: BGP RIB Collection

[Nick Hilliard <nick () foobar org>]

On 27/02/2013 03:51, Randy wrote:
> *received-routes*?
> If you still enable soft-reconfig-inbound on your routers(customer-facing sessions not withstanding), you most 
> certainly hate your routers more than OP...;-)

it impacts memory, but if your management plane has enough memory to handle
it, it's a useful debugging tool.  For sure, it's the first thing I throw
out if the management plane RAM runs short.

SNMP polling of large router lists can work out as O(n^2) CPU usage if the
router stores the polled objects as linked lists or in some cases, in tree
structures.  This is because snmpgetnext cannot maintain a pointer to the
next object, which in some situations will mean a complete tree walk
operation.  So your CPU requirements will scale according to (size of
structure) * (average number of complete walks through the structure).  If
you're using linked lists, or have a naive tree implementation, "average
number of complete walks through the structure" = "size of structure" / 2
for a full tree walk.  I.e. you can require (n^2)/2 complete runs through
the structure in order to run a full snmp dump.  Obviously this isn't
always the case, but there are some well known examples of where it happens.

For all its faults, soft-reconfig-inbound only adds O(N) to RAM
requirements and almost nothing to CPU.

Nick

> ./Randy
>
> --- On Tue, 2/26/13, Nick Hilliard <nick () foobar org> wrote:
>
> > From: Nick Hilliard <nick () foobar org>
> > Subject: Re: BGP RIB Collection
> > To: "chip" <chip.gwyn () gmail com>
> > Cc: "North American Network Operators Group" <nanog () nanog org>
> > Date: Tuesday, February 26, 2013, 11:21 AM
> > On 26/02/2013 17:24, chip wrote:
> > > Currently I'm gathering this data via SNMP.
> >
> > whoa, you must really hate your router to do that to it.
> >
> > > While this works it has its draw backs, it
> > > takes approximately 20 minutes per view, its nowhere
> > near real-time, and
> > > I'm unable to gather information for IPv6.  SNMP,
> > however, is faster than
> > > screen scraping.  All of the XML based access
> > methods seem to take about
> > > the same time as well.
> >
> > cisco:
> > --
> > term len 0
> > show bgp ipv4 unicast neigh x.y.z.w received-routes
> > --
> >
> > juniper:
> > --
> > show route receive-protocol bgp x.y.z.w | no-more
> > --
> >
> > Easily scriptable using rancid or something similar. 
> > Of course, this sucks
> > because you're only seeing the route summary, not any of the
> > attributes.
> >
> > > project is still in its infancy.  BMP seems to be
> > a good solution but I've
> > > not found a working client implementation yet.  I
> > see that you can actually
> > > configure this on some Juniper gear but I can't seem to
> > locate a client to
> > > ingest the data the router produces.
> >
> > Can you provide a list of the clients that you have
> > tried?  It would save
> > people the effort of going through them and finding out the
> > same things as
> > you did.
> >
> > Nick