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    Net Flow

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    Babu Goth
    Netflow provides network traffic monitoring and analysis capabilities. It works by generating flows of packets that share common attributes which are exported from network devices and collected and analyzed. Key information in flows includes source/destination IP, ports, protocols, timestamps and routing data. Flows can be used for traffic analysis, accounting, problem identification and security applications like detecting DDoS attacks. Vendors like Cisco support netflow on their devices with different versions and configuration options. Tools like flow-tools can then be used to collect and analyze the exported netflow data.

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    © All Rights Reserved
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    Net Flow

    Uploaded by

    Babu Goth
    24 views35 pages
    Netflow provides network traffic monitoring and analysis capabilities. It works by generating flows of packets that share common attributes which are exported from network devices and collected and analyzed. Key information in flows includes source/destination IP, ports, protocols, timestamps and routing data. Flows can be used for traffic analysis, accounting, problem identification and security applications like detecting DDoS attacks. Vendors like Cisco support netflow on their devices with different versions and configuration options. Tools like flow-tools can then be used to collect and analyze the exported netflow data.

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    Netflow provides network traffic monitoring and analysis capabilities. It works by generating flows of packets that share common attributes which are exported from network devices and collected and analyzed. Key information in flows includes source/destination IP, ports, protocols, timestamps and routing data. Flows can be used for traffic analysis, accounting, problem identification and security applications like detecting DDoS attacks. Vendors like Cisco support netflow on their devices with different versions and configuration options. Tools like flow-tools can then be used to collect and analyze the exported netflow data.

    Copyright:

    © All Rights Reserved
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    24 views35 pages

    Net Flow

    Uploaded by

    Babu Goth
    Netflow provides network traffic monitoring and analysis capabilities. It works by generating flows of packets that share common attributes which are exported from network devices and collected and analyzed. Key information in flows includes source/destination IP, ports, protocols, timestamps and routing data. Flows can be used for traffic analysis, accounting, problem identification and security applications like detecting DDoS attacks. Vendors like Cisco support netflow on their devices with different versions and configuration options. Tools like flow-tools can then be used to collect and analyze the exported netflow data.

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    © All Rights Reserved
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    Download as ppt, pdf, or txt
    of 35

    Netflow Overview

    PacNOG 6
    Nadi, Fiji
    Agenda
    • Netflow
    – What it is and how it works
    – Uses and Applications
    • Vendor Configurations/ Implementation
    – Cisco and Juniper
    • Flow-tools
    – Architectural issues
    – Software, tools etc
    • More Discussion / Lab Demonstration
    Network Flows
    • Packets or frames that have a
    common attribute.
    • Creation and expiration policy – what
    conditions start and stop a flow.
    • Counters – packets,bytes,time.
    • Routing information – AS, network
    mask, interfaces.
    Network Flows
    • Unidirectional or bidirectional.
    • Bidirectional flows can contain other
    information such as round trip time,
    TCP behavior.
    • Application flows look past the headers
    to classify packets by their contents.
    • Aggregated flows – flows of flows.
    Working with Flows
    • Generating and Viewing Flows
    • Exporting Flows from devices
    – Types of flows
    – Sampling rates
    • Collecting it
    – Tools to Collect Flows - Flow-tools
    • Analyzing it
    – More tools available, can write your own
    Flow Descriptors
    • A Key with more elements will generate more
    flows.
    • Greater number of flows leads to more post
    processing time to generate reports, more
    memory and CPU requirements for device
    generating flows.
    • Depends on application. Traffic engineering vs.
    intrusion detection.
    Flow Accounting
    • Accounting information accumulated with
    flows.
    • Packets, Bytes, Start Time, End Time.
    • Network routing information – masks and
    autonomous system number.
    Flow Generation/Collection
    • Passive monitor
    • A passive monitor (usually a unix host) receives all
    data and generates flows.
    • Resource intensive, newer investments needed
    • Router or other existing network device.
    • Router or other existing devices like switch, generate
    flows.
    • Sampling is possible
    • Nothing new needed
    Passive Monitor Collection

    Workstation A Workstation B

    Flow probe connected


    to switch port in Campus
    “ traffic mirror” mode
    Router Collection
    LAN LAN

    LAN
    LAN

    Internet
    Flow collector
    stores exported flows from router.
    Passive Monitor
    • Directly connected to a LAN segment via a
    switch port in “mirror” mode, optical splitter,
    or repeated segment.
    • Generate flows for all local LAN traffic.
    • Must have an interface or monitor deployed on
    each LAN segment.
    • Support for more detailed flows – bidirectional
    and application.
    Router Collection
    • Router will generate flows for traffic that
    is directed to the router.
    • Flows are not generated for local LAN
    traffic.
    • Limited to “simple” flow criteria (packet
    headers).
    • Generally easier to deploy – no new
    equipment.
    Vendor implementations
    Cisco NetFlow
    • Unidirectional flows.
    • IPv4 unicast and multicast.
    • Aggregated and unaggregated.
    • Flows exported via UDP.
    • Supported on IOS and CatOS platforms.
    • Catalyst NetFlow is different implementation.
    Cisco NetFlow Versions
    • 4 Unaggregated types (1,5,6,7).
    • 14 Aggregated types (8.x, 9).
    • Each version has its own packet format.
    • Version 1 does not have sequence numbers – no
    way to detect lost flows.
    • The “version” defines what type of data is in the
    flow.
    • Some versions specific to Catalyst platform.
    NetFlow v1
    • Key fields: Source/Destination IP,
    Source/Destination Port, IP Protocol, ToS,
    Input interface.
    • Accounting: Packets, Octets, Start/End
    time, Output interface
    • Other: Bitwise OR of TCP flags.
    NetFlow v5
    • Key fields: Source/Destination IP,
    Source/Destination Port, IP Protocol, ToS,
    Input interface.
    • Accounting: Packets, Octets, Start/End
    time, Output interface.
    • Other: Bitwise OR of TCP flags,
    Source/Destination AS and IP Mask.
    • Packet format adds sequence numbers for
    detecting lost exports.
    NetFlow v8
    • Aggregated v5 flows.
    • Not all flow types available on all
    equipments
    • Much less data to post process, but loses
    fine granularity of v5 – no IP addresses.
    Cisco IOS Configuration
    • Configured on each input interface.
    • Define the version.
    • Define the IP address of the collector (where to
    send the flows).
    • Optionally enable aggregation tables.
    • Optionally configure flow timeout and main (v5)
    flow table size.
    • Optionally configure sample rate.
    Cisco IOS Configuration
    interface FastEthernet0/0
    description Access to backbone
    ip address 169.223.11.194 255.255.252.0
    ip route-cache flow
    duplex auto
    speed auto
    !
    interface FastEthernet0/1
    description Access to local net
    ip address 169.223.2.1 255.255.255.128
    ip route-cache flow
    duplex auto
    speed auto

    ip flow-export version 5
    ip flow-export destination 169.223.2.2 5004
    Cisco IOS Configuration
    gw-169-223-2-0#sh ip flow export
    Flow export v5 is enabled for main cache
    Export source and destination details :
    VRF ID : Default
    Destination(1) 169.223.2.2 (5004)
    Version 5 flow records
    55074 flows exported in 3348 udp datagrams
    0 flows failed due to lack of export packet
    0 export packets were sent up to process level
    0 export packets were dropped due to no fib
    0 export packets were dropped due to adjacency issues
    0 export packets were dropped due to fragmentation failures
    0 export packets were dropped due to encapsulation fixup failures
    Cisco IOS Configuration
    gw-169-223-2-0#sh ip cache flow
    IP packet size distribution (3689551 total packets):
    1-32 64 96 128 160 192 224 256 288 320 352 384 416 448 480
    .000 .483 .189 .014 .002 .003 .001 .000 .000 .000 .000 .000 .000 .000 .001

    512 544 576 1024 1536 2048 2560 3072 3584 4096 4608
    .001 .000 .008 .002 .288 .000 .000 .000 .000 .000 .000

    IP Flow Switching Cache, 278544 bytes


    26 active, 4070 inactive, 55206 added
    1430681 ager polls, 0 flow alloc failures
    Active flows timeout in 30 minutes
    Inactive flows timeout in 15 seconds
    IP Sub Flow Cache, 25800 bytes
    26 active, 998 inactive, 55154 added, 55154 added to flow
    0 alloc failures, 0 force free
    1 chunk, 2 chunks added
    last clearing of statistics never
    Cisco IOS Configuration
    ip flow-top-talkers
    top 10
    sort-by bytes

    gw-169-223-2-0#sh ip flow top-talkers

    SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Bytes


    Fa0/1 169.223.2.2 Fa0/0 169.223.11.33 06 0050 0B64 3444K
    Fa0/1 169.223.2.2 Fa0/0 169.223.11.33 06 0050 0B12 3181K
    Fa0/0 169.223.11.33 Fa0/1 169.223.2.2 06 0B12 0050 56K
    Fa0/0 169.223.11.33 Fa0/1 169.223.2.2 06 0B64 0050 55K
    Fa0/1 169.223.2.2 Local 169.223.2.1 01 0000 0303 18K
    Fa0/1 169.223.2.130 Fa0/0 64.18.197.134 06 9C45 0050 15K
    Fa0/1 169.223.2.130 Fa0/0 64.18.197.134 06 9C44 0050 12K
    Fa0/0 213.144.138.195 Fa0/1 169.223.2.130 06 01BB DC31 7167
    Fa0/0 169.223.15.102 Fa0/1 169.223.2.2 06 C917 0016 2736
    Fa0/1 169.223.2.2 Local 169.223.2.1 06 DB27 0016 2304
    10 of 10 top talkers shown. 49 flows processed.
    Cisco command summary
    • Enable CEF (done by default)
    – ip cef

    • Enable flow on each interface


    ip route cache flow OR
    ip flow ingress
    ip flow egress

    • View flows
    – show ip cache flow
    – show ip flow top-talkers
    Cisco Command Summary

    • Exporting Flows to a collector


    ip flow-export version 5 [origin-as|peer-as]
    ip flow-export destination x.x.x.x <udp-port>

    • Exporting aggregated flows


    ip flow-aggregation cache as|prefix|dest|source|proto
    enabled
    export destination x.x.x.x <udp-port>
    Flows and Applications
    Uses for Flow
    • Problem identification / solving
    – Traffic classification
    – DoS Traceback (some slides by Danny
    McPherson)
    • Traffic Analysis
    – Inter-AS traffic analysis
    – Reporting on application proxies
    • Accounting
    – Cross verification from other sources
    – Can cross-check with SNMP data
    Detect Anomalous Events: SQL
    “Slammer” Worm*
    Flow-based Detection (cont)*
    • Once baselines are built anomalous activity can be
    detected
    – Pure rate-based (pps or bps) anomalies may be legitimate
    or
    malicious
    – Many misuse attacks can be immediately recognized,
    even
    without baselines (e.g., TCP SYN or RST floods)
    – Signatures can also be defined to identify “interesting”
    transactional data (e.g., proto udp and port 1434 and 404
    octets(376 payload) == slammer!)
    – Temporal compound signatures can be defined to detect
    with higher precision
    Flow-based Commercial Tools…*
    Commercial Detection
    A Large Scale DOS attack*
    Traffic Analysis
    • Can see traffic based on source and
    destination AS
    – Source and destination AS derived
    through the routing table on the router
    – Introduces the need to run full mesh BGP
    at IXPs as well as transit and peering
    – Source and destination prefix based flows
    can be collected and plotted against
    external prefix to ASN data
    Accounting
    • Flow based accounting can be a good
    supplement to SNMP based
    accounting.
    References
    • flow-tools:
    http://www.splintered.net/sw/flow-tools

    • NetFlow Applications
    http://www.inmon.com/technology/netflowapps.php
    • Netflow HOW-TO
    http://www.linuxgeek.org/netflow-howto.php
    • IETF standards effort:
    http://www.ietf.org/html.charters/ipfix-charter.html
    References
    • Abilene NetFlow page
    http://abilene-netflow.itec.oar.net/
    • Flow-tools mailing list:
    flow-tools@splintered.net
    • Cisco Centric Open Source Community
    http://cosi-nms.sourceforge.net/related.html

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