RE: How does Internal Bypass mode work on Juniper IDP range

Hi Joel,

Good point, I'm not sure that a duplex or mdix issue was the cause of the d=
owntime in our case however.  Reason I say this is that the issue seemed to=
 disappear after half an hour, without any intervention.  This wouldn't hap=
pen if it was a duplex/MDIX issue.  However its certainly the type of gotch=
a I was hoping to find out about when posted to the mailing list.

Many Thanks

-----Original Message-----
From: Joel M Snyder [mailto:[email protected]]=20
Sent: 26 October 2010 18:25
To: Maqbool Hashim
Cc: [email protected]
Subject: Re: How does Internal Bypass mode work on Juniper IDP range

 > In bypass mode, traffic enters the IDP ingress port and is forwarded  > =
out of the egress interface without being passed to the IDP engine.

I can't speak to the Juniper IDP box, but there are a number of issues that=
 I have seen with hardware bypass.

First, depending on the equipment, you may have incorrectly made cables.=20
  Different hardware works differently, but normally the hardware bypass in=
serts a crossover between the two devices when it snaps into place.=20
Thus, depending on what you have on either end of the IPS, you may need to =
have one crossover cable on one side and a straight-through on the=20
other side.   For gig, not a problem, but if you have a device that=20
doesn't do auto-MDIX, you've got an issue.  This is the number-one problem =
I've seen and is the result of a sloppy install.

Second, you may have a negotiation problem.  These are myriad throughout th=
e networking world.  Your typical networking team member knows how to set i=
t up correctly, but if a security person without the right background did t=
he configuration, you may have (for example) one side doing auto-negotiatio=
n and the other side not, a recipe for failure (depending on how your devic=
e actually implements non-negotiated traffic)

Those two seem to cover about 90% of the issues.  The other 10% are caused =
by bad relays--the IPS box doesn't actually "snap in" to bypass mode when t=
he watchdog doesn't go off or the power disappears.

You can probably isolate to these three, or some other, by performing a pow=
er cord attenuation on the IPS device during a sanctioned downtime.

Unless the Juniper is badly flawed and in need of a forklift upgrade, the M=
AC table issue is non-existent; the IPS should not be interfering with the =
MAC on either side of it.

jms


On 10/26/10 6:29 PM, Maqbool Hashim wrote:
> Hi,
>
> I recently saw an outage in a network that had a Juniper IPS device deplo=
yed.  The outage consisted of tcp sessions timing out for users, ping conne=
ctivity was not confirmed.  The IPS is deployed in transparent mode and Int=
ernal Bypass is enabled on the ingress and egress interface pair that make =
up the virtual router.   My understanding of the internal bypass feature is=
 as follows as per the Juniper documentation:
>
> In bypass mode, traffic enters the IDP ingress port and is forwarded out =
of the egress interface without being passed to the IDP engine.  The ingres=
s and egress interface join mechanically to form a circuit in order to cont=
inue passing traffic through the IPS device.  Effectively the interfaces be=
come a piece of wire.  Bypass mode is triggered by a timing mechanism durin=
g system failure or shutdown.  This feature has been enabled to optimise av=
ailability and ensure that network outages do not occur because the IDS cra=
shes/fails/ or cannot process packets fast enough.
>
> I'm trying to determine the cause of the outage we suffered, which is why=
 I wanted a deeper understanding of internal bypass and the effects it may =
or may not have on the surrounding network architecture.  The outage I saw =
occurred at around the same time the IPS box rebooted and consequently ente=
red bypass mode.  Bypass mode was only activated for a minute from the sysl=
og entries, however the outage we saw lasted for approximately half an hour=
.
>
> So my questions regarding bypass mode are:
>
> 1) During bypass mode the link status on the IPS interfaces will be down.=
  Will the switch interfaces connected to the IPS device remain up as they =
are now connected to each other through the IPS (piece of wire) rather than=
 to the IPS interfaces?
>
> 2)  If the switch interfaces are now connected to each other rather than =
the IPS what about mac forwarding tables?  Is it possible that the forwardi=
ng tables on the switches get confused?
>
> 3) Any specific session based issues that could be caused by the IPS devi=
ce engaging and disengaging internal bypass mode?
>
> My feeling is that the issues might be caused by how the network environm=
ent responds to the IPS engaging/disengaging internal bypass mode rather th=
an an issue with the IPS device.  I'm just looking for some guidance on any=
 gotchas that I should be aware of with regards to the network environment =
when the IPS device triggers bypass mode.
>
> Thanks
>
> Maq
>
>
>
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--
Joel M Snyder, 1404 East Lind Road, Tucson, AZ, 85719
Senior Partner, Opus One       Phone: +1 520 324 0494
[email protected]                http://www.opus1.com/jms

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