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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

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