NAME¶
flow-tools-examples — Example usage of flow-tools.
EXAMPLE - Configuring Cisco IOS Router¶
NetFlow is configured on each input interface, then global commands are used to
specify the export destination. To ensure a consistant source address address
Loopback0 is configured as the export source.
ip cef distributed
ip flow-export version 5 origin-as
ip flow-export destination 10.0.0.100 5004
ip flow-export source Loopback0
interface Loopback0
ip address 10.1.1.1 255.255.255.255
interface FastEthernet0/1/0
ip address 10.0.0.1 255.255.255.0
no ip directed-broadcast
ip route-cache flow
ip route-cache distributed
Many other options exist such as aggregated NetFlow and sampled NetFlow which
are detailed at
(link to URL http://www.cisco.com) .
EXAMPLE - Configuring Cisco CatIOS Switch¶
Some Cisco Catalyst switches support a different implementation of NetFlow that
is performed on the supervisor. With the cache based forwarding model which is
implemented in the Catalyst 55xx with Route Switch Module (RSM) and NetFlow
Feature Card (NFFC), the RSM processes the first flow and the remaining
packets in the flow are forwarded by the Supervisor. This is also implemented
in the early versions of the 65xx with MSFC. The deterministic forwarding
model used in the 65xx with MSFC2 do not use NetFlow to determine the
forwarding path, the flow cache is only used for statistics as in the current
IOS implementations. In all of of the above configurations flow exports arrive
from both the RSM/MSFC and the Supervisor engines as distinct streams. In the
worst cast the RSM exports in version 5 and the Supervisor exports in version
7. Fortunately flow-capture and flow-receive can sort all this out by
processing flows from both sources and converting them to a common export
format.
The router side running IOS is configured identically to the example given
above. The CatIOS NetFlow Data Export configuration follows:
set mls flow full
set mls nde version 7
set mls nde 10.0.0.1 9800
set mls nde enable
When the 65xx is running in Native mode, from a users perspective the switch is
only running IOS.
More detailed examples can be found on Cisco's web site
(link to URL
http://www.cisco.com) .
EXAMPLE - Configuring Juniper Router¶
Juniper supports flow exports by the routing engine sampling packet headers and
aggregating them into flows. Packet sampling is done by defining a firewall
filter to accept and sample all traffic, applying that rule to the interface,
then configuring the sampling forwarding option.
interfaces {
ge-0/3/0 {
unit 0 {
family inet {
filter {
input all;
output all;
}
address 10.0.0.1/24;
}
}
}
firewall {
filter all {
term all {
then {
sample;
accept;
}
}
}
}
forwarding-options {
sampling {
input {
family inet {
rate 100;
}
}
output {
cflowd 10.0.0.100 {
port 9800;
version 5;
}
}
}
}
Other options exist such as aggregated flows which are detailed at
(link to
URL http://www.juniper.net) .
EXAMPLE - Network topology and flow.acl¶
The network topology and flow.acl will be used for many of the examples that
follow. Flows are collected and stored in
/flows/R.
ISP-A ISP-B
+ +
+ +
IP=10.1.2.1/24 + + IP=10.1.1.1/24
ifIndex=2 + + ifIndex=1
interface=serial1/1 + + interface=serial0/0
-----
| R | Campus Router
-----
+ +
IP=10.1.4.1/24 + + IP=10.1.3.1/24
ifIndex=4 + + ifIndex=3
interface=Ethernet1/1 + + interface=Ethernet0/0
+ +
Sales Marketing
ip access-list standard sales permit 10.1.4.0 0.0.0.255
ip access-list standard not_sales deny 10.1.4.0 0.0.0.255
ip access-list standard marketing permit 10.1.3.0 0.0.0.255
ip access-list standard not_marketing deny 10.1.3.0 0.0.0.255
ip access-list standard campus permit 10.1.4.0 0.0.0.255
ip access-list standard campus permit 10.1.3.0 0.0.0.255
ip access-list standard not_campus deny 10.1.4.0 0.0.0.255
ip access-list standard not_campus deny 10.1.3.0 0.0.0.255
ip access-list standard evil_hacket permit host 10.6.6.6
ip access-list standard spoofer permit host 10.9.9.9
ip access-list standard multicast 224.0.0.0 15.255.255.255
EXAMPLE - Finding spoofed addresses¶
A common problem on the Internet is the use of "spoofed" (addresses
that are not assigned to an organization) for use in DoS attacks or
compromising servers that rely on the source IP address for authentication.
Display all flow records that originate from the campus and are sent to the
Internet but are not using legal addresses.
flow-cat /flows/R | flow-filter -Snot_campus -I1,2 | flow-print
Summary of the destinations of the internally spoofed addresses sorted by
octets.
flow-cat /flows/R | flow-filter -Snot_campus -I1,2 | flow-stat -f8 -S2
Summary of the sources of the internally spoofed addresses sorted by flows.
flow-cat /flows/R | flow-filter -Snot_campus -I1,2 | flow-stat -f9 -S1
Summary of the internally spoofed sources and destination pairs sorted by
packets.
flow-cat /flows/R | flow-filter -Snot_campus -I1,2 | flow-stat -f10 -S4
Display all flow records that originate external to the campus that have campus
addresses. Many times these can be attackers trying to exploit host based
authentication mechanisms like unix r* commands. Another common source is
mobile clients which send packets with their campus addresses before obtaining
a valid IP.
flow-cat /flows/R | flow-filter -Scampus -i1,2 | flow-print
Summary of the destinations of the externally spoofed addresses sorted by
octets.
flow-cat /flows/R | flow-filter -Scampus -i1,2 | flow-stat -f8 -S2
EXAMPLE - Locate hosts using or running services¶
Find all SMTP servers active during the collection period that have established
connections to the Internet. Summarize sorted by octets.
flow-cat /flows/R | flow-filter -I1,2 -P25 | flow-stat -f9 -S2
Find all outbound NNTP connections to the Internet. Summarize with source and
destination IP sorted by octets.
flow-cat /flows/R | flow-filter -I1,2 -P119 | flow-stat -f10 -S3
Find all inbound NNTP connections to the Internet. Summarize with source and
destination IP sorted by octets.
flow-cat /flows/R | flow-filter -i1,2 -P119 | flow-stat -f10 -S3
EXAMPLE - Multicast usage¶
Summarize Multicast S,G where sources are on campus.
flow-cat /flows/R | flow-filter -Dmulticast -I1,2 | flow-stat -f10 -S3
Summarize Multicast S,G where sources are off campus.
flow-cat /flows/R | flow-filter -Dmulticast -i1,2 | flow-stat -f10 -S3
EXAMPLE - Find scanners¶
Find SMTP scanners with flow-dscan. This will also find SMTP clients which try
to contact many servers. This behavior is characterized by a recent Microsoft
worm.
touch dscan.suppress.src dscan.suppress.dst
flow-cat /flows/R | flow-filter -P25 | flow-dscan -b
AUTHOR¶
Mark Fullmer maf@splintered.net
SEE ALSO¶
flow-tools(1)