Paul, I'm confused about your comments regarding packets "tunneled within
HSRP". HSRP is Cisco's Hot Standby Routing Protocol. It's a multicast
virtual routing interface technology for making L3 gateways on a local
subnet highly available, not a tunneling or packet encapsulation protocol as
you suggest. I'm guessing you meant 802.1q or ISL vs. HSRP, no? Or is there
some new covert channel involving HSRP ISS has discovered that the rest of
us are unaware of?
Anyway, usually* the best bet is to SPAN the various VLANs that you're
wanting to monitor into a single destination port on the switch/router.
Don't bother trying to monitor the physical aggregated ports themselves.
Logical VLAN monitoring is almost always easier.
Most vendors offer the option to either mirror Ethernet frames transiting
the trunk with or without tagging. You'll usually want to enable tagged
frames as modern sensor technologies will make use of the VLAN ID contained
within the tag.
If you have two or more switch/routers that are HSRP enabled just plug the
SPAN/mirror output from these devices into multiple ports offered on a
single sensor (pretty much *all* vendors support port aggregation at this
point). It's important that you avoid asymmetric routing. Given the fact
that packets can come into a subnet on the secondary HSRP router and leave
on the primary, you MUST monitor both HSRP devices using a single sensor.
* The only exception to this is 1) the switch/router vendor doesn't support
monitoring of logical VLANs or 2) duplicate Ethernet frames are a major
concern. SPANing multiple logical VLANs in a single switch *can* cause
multiple packets to be mirrored to a single egress mirror port.
- Adam P.
On 9/7/06 7:26 PM, "Palmer, Paul (ISSAtlanta)" <PPalmer@iss.net> wrote:
Jan,
*** I work for ISS ***
This is likely a vendor specific question.
Some vendors can monitor the HSRP traffic directly, while others will
not be able to reliably recognize attacks tunneled within HSRP. If your
vendor cannot identify attacks within HSRP, you would either need to
chose a different location for the IDS where HSRP is not present or
chose another vendor.
Some vendors aggregate the packets from their various adapters, while
others do not. In some cases, they do so only partially. Ask your vendor
whether they support PortChannel, EtherChannel, etc. and how they
support it. If the adapters are aggregated, the best thing would be to
place a tap on each link in the channel/bundle and feed the packets from
all of the links to the same IDS. That is, you would place a tap on each
link and feed the output from each tap to a different input adapter on
the same IDS. If the IDS cannot aggregate adapters, you will need to use
a SPAN port capable of handling the full bandwidth of the channel, look
at placing the IDS elsewhere on the network where PortChannel is not
used, or chose another vendor.
I hope this helps.
Paul
P.S. Since I work for ISS I would be remiss if I did not mention that
ISS products do recognize attacks tunneled within HSRP and do aggregate
the packets from their adapters.
-----Original Message-----
From: Scholten, Jan [mailto:jan.scholten@siemens.com]
Sent: Thursday, September 07, 2006 6:27 AM
To: focus-ids@securityfocus.com
Subject: IDS in a loadbalanced Network
Hi!
While searching for a matching IDS I encountered some problems.
Having a network structure with lots of seperate Vlans and/or DMZs
networks, i am wondering what is the best way to place an IDS in a
redundant L3Switch/router (C6506/7300) with HSRP and PortChannel
Loadbalancing for Vlans.
Is there a bestpractice how to place an ids in a vlan, using a span port
on each of the devices (running in active/active), or is there a better
solution?
Regards from Germany
Jan Scholten
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to learn more.
------------------------------------------------------------------------
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Test Your IDS
Is your IDS deployed correctly?
Find out quickly and easily by testing it
with real-world attacks from CORE IMPACT.
Go to http://www.securityfocus.com/sponsor/CoreSecurity_focus-ids_040708
to learn more.
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