CAM (Layer 2)

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Applied Cisco Networking(CCNP BCMSN)Unit 4MLS

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CAM (Layer 2)

MAC1 MAC2 MAC3 MAC4

CAM P1: MAC1, MAC2P2: MAC3, MAC4

P1 P2

Content Addressable Memory (CAM). These days bridges are hardly ever used, and switches are used instead. The CAM contains a table of MAC addresses for each port, and forwards as required.

Src: MAC1 Dest: MAC4

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Showing CAM table

MAC1 MAC2 MAC3 MAC4

CAM P1: MAC1, MAC2P2: MAC3, MAC4

P1 P2

To show the CAM table:

Swi tch# sh mac address- tabl e dynami c Mac Address Tabl e- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Vl an Mac Address Type Ports- - - - - - - - - - - - - - - - - - - - - - - - - - - - 1 000d. 298e. a19a DYNAMI C Gi 0/ 2 1 0011. 5c5e. ac41 DYNAMI C Fa0/ 3 1 0011. 5c5e. ac42 DYNAMI C Fa0/ 4 10 000d. 298e. a19a DYNAMI C Gi 0/ 2 20 000d. 298e. a19a DYNAMI C Gi 0/ 2

Src: MAC1 Dest: MAC4

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External Route Processing

192.168.0.1 192.168.1.1

# confi g t( confi g) # r out er r i p( confi g- r out er ) # net wor k 192. 168. 0. 0( confi g- r out er ) # net wor k 192. 168. 1. 0( confi g- r out er ) # exi t( confi g) # i nt f a0/ 1( confi g- i f ) # i p addr ess 192. 168. 0. 254 255. 255. 255. 0( confi g- i f ) # no shut down( confi g- i f ) # exi t( confi g) # i nt f a0/ 2( confi g- i f ) # i p addr ess 192. 168. 1. 254 255. 255. 255. 0( confi g- i f ) # no shut down

( confi g- i f ) # exi tF

a0/1

Fa0

/2

Default gateway set to the router

port

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Router-on-a-stick

192.168.0.1 192.168.1.1

# confi g t( confi g) # r out er r i p( confi g- r out er ) # net wor k 192. 168. 0. 0( confi g- r out er ) # net wor k 192. 168. 1. 0( confi g- r out er ) # exi t( confi g) # i nt f a0/ 1. 1( confi g- i f ) # i p addr ess 192. 168. 0. 254 255. 255. 255. 0( confi g- i f ) # encapsul at i on dot 1q 1( confi g- i f ) # exi t( confi g) # i nt f a0/ 1. 2( confi g- i f ) # i p addr ess 192. 168. 1. 254 255. 255. 255. 0( confi g- i f ) # encapsul at i on dot 1q 2

( confi g- i f ) # exi t

Fa

0/1

Default gateway set to the router

port

Fa

0/1

.1

Fa

0/1

.2

Sub-interfaces required to

encapsulate the VLAN

information between the two VLANs

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Internal Route Processing

192.168.0.1 192.168.1.1

# confi g t( confi g) # i p r out i ng( confi g) # r out er r i p( confi g- r out er ) # net wor k 192. 168. 0. 0( confi g- r out er ) # net wor k 192. 168. 1. 0( confi g- r out er ) # exi t( confi g) # vl an 1( confi g- vl an) # exi t( confi g) # i nt vl an 1 ( confi g) # i p addr ess 192. 168. 0. 254 255. 255. 255. 0( confi g- vl an) # exi t( confi g) # vl an 2( confi g- vl an) # exi t( confi g) # i nt vl an 2( confi g- i f ) # i p addr ess 192. 168. 1. 254 255. 255. 255. 0( confi g- i f ) # exi t( confi g) # i nt f a0/ 1( confi g- i f ) # swi t chpor t mode access( confi g- i f ) # swi t chpor t access vl an 1( confi g- i f ) # exi t( confi g) # i nt f a0/ 2( confi g- i f ) # swi t chpor t mode access( confi g- i f ) # swi t chpor t access vl an 2

( confi g- i f ) # exi t

VLAN 1:192.168.0.254

VLAN 2:192.168.1.254

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Layer 3 operation

# confi g t(confi g)# i p routi ng

(confi g)# i nt f a0/ 1(confi g- i f )# no swi tchport mode access(confi g- i f )# i p address 192. 168. 0. 254 255. 255. 255. 0( confi g- i f ) # no shut down

FA0/1

192.168.0.1 192.168.0.2

192.168.0.254FA0/1

192.168.1.254FA0/1192.168.2.254

192.168.1.1 192.168.1.2 192.168.2.1 192.168.2.2

192.168.4.0 192.168.5.0

.1 .2 .1 .2

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( confi g) # i p r out i ng( confi g) # vl an 1( confi g- vl an) # exi t( confi g) # i nt vl an 1 ( confi g- vl an) # i p addr ess 10. 0. 0. 254 255. 255. 255. 0

( confi g- vl an) # exi t

( confi g) # i nt f a0/ 2( confi g- i f ) # swi t chpor t t r unk encapsul at i on dot 1q( confi g- i f ) # swi t chpor t t r unk nat i ve vl an 1( confi g- i f ) # swi t chpor t t r unk al l owed vl an 1, 2( confi g- i f ) # swi t chpor t mode t r unk( confi g- i f ) # swi t chpor t nonegot i at e

FA0/1

192.168.0.1 192.168.0.2

VLAN 1:192.168.0.254

FA0/1 FA0/1

192.168.1.1 192.168.1.2 192.168.2.1 192.168.2.2

VLAN 2:192.168.2.254FA0/2 FA0/2

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MLS

MLS (Multilayered Switching). 3550, 4500 and 600- series switches can also forward frames based on Layer 3 and 4 information contained in packets. Two types:· Route cache.· Topology-based.

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Route-cache switching

Route-cacheRequires a route processor (RP) and a switch engine (SE).

· The RP process the first packet to determine its destionation.

· The SE listens to this and the resulting destination, and sets up a shortcut entry in its MLS cache.

· The SE forwards all subsequent packets in the same traffic flow based on shortcut entries in its cache.

AKA: Netflow LAN switching, flow-based or demand-based switching, and "route once, switch many.

Route processor

(RP)

MLS cache

SwitchEngine (SE)First-time

route

MLS cacheupdate

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Topology-based (CEF)

Topology-basedThis method uses specialized hardware. It uses Layer 3 routing information to build and prepopulate a single database for the entire network topology.

This is a table lookup in hardware and is used to forward packets at high rates. The longest match found in the database is used as the correct Layer 3 destination.

As routing topology change over time, the database contained in the hardware is continually updated.

Cisco Express Forwarding (CEF)

SwitchProcessor

Routinginformation

Forwarding Information Base (FIB)

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MultiLayer Catalyst Switch OperationsSecurity ACLs

Inbound/Outbound (TCAM)

QoS ACLsClassification/Policing

(TCAM)

L3 Forwarding Table (FIB)

L2 Forwarding Table(CAM)

IngressQueues

PacketRe-writer

MAC address Egress Port VLAN

000d. 298e. a19a Gi0/2 1

Swi tch# sh mac address- tabl e dynami c Mac Address Tabl e- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Vl an Mac Address Type Ports- - - - - - - - - - - - - - - - - - - - - - - - - - - - 1 000d. 298e. a19a DYNAMI C Gi 0/ 2 1 0011. 5c5e. ac41 DYNAMI C Fa0/ 3 1 0011. 5c5e. ac42 DYNAMI C Fa0/ 4 10 000d. 298e. a19a DYNAMI C Gi 0/ 2 20 000d. 298e. a19a DYNAMI C Gi 0/ 2

0011. 5c5e. ac41 Fa0/3 1

CAM table

IP address Next-hop IP Next-hop MAC

192. 168. 0. 0 192.168.10.1 000d. 298e. a19a

FIB table

Egress Port

Fa0/1

# show i p cefPr efi x Next Hop I nt er f ace0. 0. 0. 0/ 0 192. 168. 1. 5 f a0/ 10. 0. 0. 0/ 32 r ecei ve192. 168. 0. 0/ 24 192. 168. 10. 1 f a0/ 1192. 168. 2. 0/ 30 192. 168. 10. 1 f a0/ 2192. 168. 3. 0/ 30 192. 168. 10. 1 f a0/ 3192. 168. 4. 0/ 24 192. 168. 10. 1 f a0/ 1192. 168. 5. 0/ 30 192. 168. 10. 1 f a0/ 2

# show i p cef summaryI P CEF wi t h swi t chi ng ( Tabl e Ver si on 1267) , fl ags=0x0239 r out es, 0 r er esol ve, 0 unr esol ved ( 0 ol d, 0 new) , peak 33 i nst ant r ecur si ve r esol ut i ons, 0 used backgr ound pr ocess239 l eaves, 153 nodes, 195448 byt es, 776 i nser t s, 537 i nval i dat i ons0 l oad shar i ng el ement s, 0 byt es, 0 r ef er encesuni ver sal per - dest i nat i on l oad shar i ng al gor i t hm, i d 9C1B7D1D3( 0) CEF r eset s, 483 r evi si ons of exi st i ng l eavesResol ut i on Ti mer : Exponent i al ( cur r ent l y 1s, peak 1s)485 i n- pl ace/ 0 abor t ed modi fi cat i onsr ef count s: 40214 l eaf , 39424 node

Tabl e epoch: 0 ( 239 ent r i es at t hi s epoch)

Adj acency Tabl e has 3 adj acenci es

192. 168. 2. 0 192.168.10.1 000d. 298e. a19a Fa0/2

EgressQueues

Permit/deny/other

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Adjacency tables



IngressQueues

PacketRe-writer

CEF mai ntai ns an adj acency tabl e f rom MAC addresses l earnt through ARP. Thi s tabl e contai ns the MAC address rewri te i nformati on and the desti nati on port. The next- hop address i s the adj acency i nformati on.

· Swi tch detects i ts own desti nati on MAC address.

· I t l ooks up the desti nati on I P address i n the CEF tabl e.

· The fi rst match i n the CEF tabl e poi nts to an adj acency entry that contai ns the MAC rewri te i nformati on and desti nati on i nterface.

· The swi tch then rewri tes the packet and sends i t out the desti nati on i nterface.

Adjacency tables

IP address Next-hop IP Next-hop MAC

192. 168. 0. 0 192.168.10.1 000d. 298e. a19a

FIB table

Egress Port

Fa0/1192. 168. 2. 0 192.168.10.1 000d. 298e. a19a Fa0/2

EgressQueues

Next-hop MAC

000d. 298e. a19a

Port

Fa0/1000d. 298e. a19a Fa0/2

#show adj acency

Pr ot ocol I nt er f ace Addr ess

I P Gi gabi t Et her net 0/ 1 192. 168. 0. 1 ( 11120)I P Fast Et her net 0/ 1 192. 168. 2. 1 ( 7)I P Fast Et her net 0/ 2 100. 1. 1. 1 ( 2005)

#show adj acency detai l

Pr ot ocol I nt er f ace Addr essI P Gi gabi t Et her net 0/ 1 192. 168. 0. 1( 11120) 0 packet s, 0 byt es 000d298ea19a 00D00624440A0800 ARP 00: 05: 40 Epoch: 0

I P Fast Et her net 0/ 1 192. 168. 2. 1 ( 7) 0 packet s, 0 byt es 00D0BCF107C8 00D00624440A0800 ARP 00: 39: 20 Epoch: 0

IP address

192. 168. 0. 1192. 168. 2. 1

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Change of data frame

FA0/1

FA0/2

FA0/2

FA0/3

192.168.1.21111.2222.1112

192.168.1.11111.2222.1111

192.168.2.11111.2222.1113

192.168.2.21111.2222.1114

192.168.3.21111.2222.1115

192.168.3.11111.2222.1116

Src IP 192.168.1.1Src MAC: 1111.2222.1111Dest IP 192.168.3.1Dest MAC: 1111.2222.1112



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Level 2 information

FA0/1

FA0/2

FA0/2

FA0/3

192.168.1.21111.2222.1112

192.168.1.11111.2222.1111

192.168.2.11111.2222.1113

192.168.2.21111.2222.1114

192.168.3.21111.2222.1115

192.168.3.11111.2222.1116


MAC address Egress Port VLAN

1111. 2222. 1111 Fa0/1 1

Swi tch# sh mac address- tabl e Mac Address Tabl e- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Vl an Mac Address Type Ports- - - - - - - - - - - - - - - - - - - - - - - - - - - - 1 1111. 2222. 1111 DYNAMI C FA0/ 1 1 1111. 2222. 1114 DYNAMI C FA0/ 2 1 1111. 2222. 1112 STATI C FA0/ 1 1 1111. 2222. 1113 STATI C FA0/ 2

Tot al Mac Addr esses f or t hi s cr i t er i on: 4

1111. 2222. 1114 Fa0/2 1

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Adjacency table

FA0/1

FA0/2

FA0/2

FA0/3

192.168.1.21111.2222.1112

192.168.1.11111.2222.1111

192.168.2.11111.2222.1113

192.168.2.21111.2222.1114

192.168.3.21111.2222.1115

192.168.3.11111.2222.1116


#show adj acency

Pr ot ocol I nt er f ace Addr ess

I P Fast Et her net 0/ 2 192. 168. 2. 2 ( 7)

#show adj acency detai l

Pr ot ocol I nt er f ace Addr essI P Fast Et her net 0/ 1 192. 168. 2. 2( 7) 0 packet s, 0 byt es 111122221114 1111222211130800 ARP 00: 05: 40 Epoch: 0

The value in parentheses, 7, refers to the number of times an FIB entry points to an adjacency entry

The first 12 characters, 111122221114, is the MAC address of the destination next-hop interface (destination MAC address rewrite).

The next 12 characters, 111122221113 are the MAC address of the source interface of the packet (source MAC address rewrite).

The last four characters (0x0800) represent an IP packet.

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CEF table

FA0/1

FA0/2

FA0/2

FA0/3

192.168.1.21111.2222.1112

192.168.1.11111.2222.1111

192.168.2.11111.2222.1113

192.168.2.21111.2222.1114

192.168.3.21111.2222.1115

192.168.3.11111.2222.1116


# show i p cefPr efi x Next Hop I nt er f ace0. 0. 0. 0/ 0 192. 168. 2. 2 f a0/ 20. 0. 0. 0/ 32 r ecei ve192. 168. 3. 0/ 24 192. 168. 2. 2 f a0/ 2192. 168. 2. 2/ 32 at t ached f a0/ 2192. 168. 1. 0/ 24 at t ached f a0/ 1224. 0. 0. 0/ 4 dr op 224. 0. 0. 0/ 24 r ecei ve

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TCAMs

TCAM (Ternary Content Addressable Memory )

In normal ACL process, the ACLs are evaluated one at a time, which leads to a delay. In multilayer switches all the matching process that ACLs provide is implemented in hardware. Thus TCAM allows the packet to be evaluated against an entire access list in a single table lookup.

There are also multiple TCAMs for inbound and outbound security and QoS ACLs in parallel with with a Layer 2 or Layer 3 forwarding decision.

Security ACLsInbound/Outbound

(TCAM)

QoS ACLsClassification/Policing

(TCAM)



IngressQueues

PacketRe-writer

EgressQueues

Permit/deny/other

CAM (Layer 2)

Documents

Transcript of CAM (Layer 2)