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S7C7 – Multilayer Switching

S7C7 – Multilayer Switching. Design and Configuration. Multilayer Switching Overview. Higher performance level First packet though is routed Rest of packet stream is switched

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S7C7 – Multilayer Switching

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  1. S7C7 – Multilayer Switching Design and Configuration

  2. Multilayer Switching Overview • Higher performance level • First packet though is routed • Rest of packet stream is switched • Frame forwarding and rewrite function is moved to hardware and layer 3 switching takes over task formerly done by routers • MLS uses RSM and the engine • Any switching path on the RSM will work • NetFlow switching is different

  3. What MLS NEEDS – We don’t have • 2926G, 5000, 6000 with supervisor engine software >=4.1(1) • Cisco IOS >=11.3 • Supervisor Engine III or G • Route Switch Feature Card (RSFC)

  4. MLS Components • Multilayer Switching Switch Engine (MLS-SE) • An NFFC residing on a Supervisor Engine III card • Multilayer Switching Route Processor (MLS-RP) • An RSM, RSFC, MSFC, or external router • Multilayer Switching Protocol (MLSP) • Operates between MLS-SE and MLS-RP • Advertises routing changes, VLANS, and MAC addresses

  5. MLS-RP Advertisements • Hello messages sent every 15 seconds to all switches in network • MAC addresses used by MLS-RP on all interfaces participating in MLS • Access List information • Route additions and deletions • Processed only by layer 3 switches; others pass messages downstream • Uses Cisco Group Management Protocol (CGMP) multicast address

  6. MLS Caching • Switch receives frame - looks at destination MAC • Recognizes address as MLS-RP address because of hello message information • Checks MLS cache to determine is MLS flow is already established • For initial packet, forwards frame to route processor – creates candidate entry in cache • Route processor consults routing table • If it finds entry, constructs a new Layer 3 header & enters MAC address of destination host or next-hope route processor as destination MAC address • Route processor forwards frame back to MLS-SE

  7. MLS Cache Explanation • Xtags enable switch to know frame came from same route processor for same flow • Subsequent frames follow first • MLS-SE must see both sides of flow from source to destination to perform layer 3 switching • Switch will then rewrite layer 3 frame header and rewrite switches layer 3 packets so they appear to have been routed by route processor • Switch forwards rewritten frame to destination MAC address • When traffic for flow ceases, the entry ages out (remains in cache for only 5 seconds)

  8. Stopping MLS • Any command that forces router to examine packet disables MLS • IP tcp header-compression • No IP routing • IP security

  9. Steps to Configure MLS • Enable MLSP • Assign VLAN ID to route processor interface • Add interfaces to same VLAN Trunking protocol (VTP) domain as switch • Enable MLS on every interface • Configure MLS Management interface • Verify MLS on MLS-RP

  10. Displaying VTP Domain Information • Show mls rp vtp-domain DOMAINNAME • Name of vtp domain • Statistical information for each vtp domain • Number of management interfaces defined for MLS-RP • Number of VLANS in domain and ID of each • MLS-Ses which router or RSM knows • MAC address of each switch in domain

  11. Verifying MLS-RP • Show mls rp • Globally enabled or disabled • MLS ID for MLS-RP • MLS IP address for MLS-RP • MLS flow mask • Name of VTP domain • Statistical information for VTP domain • Management interfaces defined for MLS-RP • VLANs configured for MLS • VLAN ID for MAC address • MLS-Ses to which RSM or router is connected • MAC address of each switch

  12. Flow Masks • Used by MLS-SE to determine how packets are compared to MLS entries in the MLS cache • Based on access lists configured on MLS router • Learned through MLSP messages • Supports only one flow mask • Destination IP • Source-Destination IP • IP flow – includes protocol and protocol ports • Set mls flow [destination|destination-source|full] • Does not require an access list on route processor • Log, reflexive, and established options not allowed

  13. MLS-SE Configuration and Caching • MLS Caching • Candidate entries remain in cache for 5 seconds • MLS entry deleted after aging time(default 256 seconds) • MLS entries can be purged by other events • Applying access lists, routing changes, disabling MLS • Configuration • Set mls enable • Set mls agingtime 200 • Set mls agingtime fast 32 pkt_threshold 3 • Set mls include n.n.n.n • Clear mls include all

  14. Verifying MLS Configuration • Show mls • Status of mls • Aging time for cache entries • Fast aging time and packet threshold • Flow mask • Total packets switched • Active MLS entries in cache • Netflow enabled ports and hosts • MLS-RP IP address, MAC accress, XTAG, & VLANs

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