Router is an L3 device, but some models (such as Cisco 1700 router), we can attach the WIC-4ESW which is L2 switching card.

as per the offical Cisco datasheet: The WIC-4ESW interface card is a Layer 2 Ethernet switch with Layer 3 routing capability. (Layer 3 routing is forwarded to the host, and is not actually performed at the switch.)

my question is, does the router use the ARP table for the L2 switching (instead of MAC table as usually done on "regular" switch) - i'm specficlly referring to the devices connected to the WIC-4ESW card?

  • L2 switching does not use ARP or even have an ARP table. ARP relates a L2 address to a L3 address, and L2 switching does not use L3. A L2 switch has a MAC address table that relates a switch interface to a MAC address, and it does not use L3 addresses.
    – Ron Maupin
    Jan 31, 2022 at 15:49

2 Answers 2


The WIC-4ESW is a small, very dumb switch -- looks like it's entirely an FPGA and not an off-the-shelf switch SoC. One thing to note, the WIC interface is about 8Mbps, so layer-3 through put will be eye wateringly slow. Layer-2 switching will be pretty good, tho.

Given it isn't a "Real Switch"(tm). It's not as simple as "show mac address-table". But you can see the internal MAC table:

blue-gw#show controllers fastEthernet 1
ESW WIC FPGA Version: 19

 Status = 0x1300            Control = 0x1
Intr Event= 0x1     SMI Spd = 0x81

Port (CPU PORT) Registers:
Status     : 0x3300         Control     : 0x6173
Identifier : 0x1531         Vlan Map    : 0x5F
VID and PRI: 0x1            Rate Control: 0x30
Port Asc Vt: 0x20
TX counter : 0x2BE3         RX counter  : 0x260F

    Tx Interrupts = 18347043, Tx BD Service Count = 21177874
    Rx Interrupts = 15339760, Rx BD Service Count = 19606005

 Interface FastEthernet1

PHY (0) Register:
Control    : 0x3100         Status      : 0x786D
Identifier : 0x141  0xC87
Auto Neg   : 0x5E1          Auto Neg Exp: 0x5
Link Partner Ability: 0x41E1        Link Partner Nxt Pg: 0x0
PHY ctrl   : 0x4130         PHY status  : 0x6C40
INTR enable: 0x400          INTR status : 0x0

Port (0) Registers:
Status     : 0x7B00         Control     : 0x73
Identifier : 0x1531         Vlan Map    : 0x47E
VID and PRI: 0x1            Rate Control: 0x4530
Port Asc Vt: 0x1
TX counter : 0x2608         RX counter  : 0x2C06

Global Registers:
Status   : 0x854            Control  : 0x402

   Mac Address     |   Ports   |  Entry State  
00-02-17-61-CB-4F  |    0x20   |     0x0F
01-00-0C-CC-CC-CC  |    0x20   |     0x0E
01-00-0C-CC-CC-CD  |    0x20   |     0x0E
01-00-0C-CD-CD-CE  |    0x20   |     0x0E
01-80-C2-00-00-00  |    0x20   |     0x0E
08-00-20-89-AF-85  |    0x01   |     0x0D
09-00-2B-01-00-01  |    0x20   |     0x0E

Entries in VTU : 1
VLAN <1>  
 Port |        Member Tag          |   Port State  |  DbNum 
  0   |  EGRESS UNTAGGED   <0x02>  |    IGNORED    |   0
  1   |  NOT A MEMBER      <0x01>  |    IGNORED    |   0
  2   |  NOT A MEMBER      <0x01>  |    IGNORED    |   0
  3   |  NOT A MEMBER      <0x01>  |    IGNORED    |   0
  4   |  NOT A MEMBER      <0x01>  |    IGNORED    |   0
  5   |  EGRESS TAGGED     <0x03>  |    IGNORED    |   0

blue-gw#show arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  xx.x.x.3                9   0800.2089.af85  ARPA   Vlan1
Internet  xxx.xx.252.2            -   0002.1761.cb4f  ARPA   FastEthernet0
Internet  xxx.xx.252.8            0   00e0.8129.cdcc  ARPA   FastEthernet0
Internet  xxx.xx.252.14         181   001b.d510.0408  ARPA   FastEthernet0
Internet  xx.x.x.254              -   0002.1761.cb4f  ARPA   Vlan1

There's only one machine plugged into that port. And it's the only port in use.

  • According the manual, it does support "show mac address table"
    – Ron Trunk
    Jan 31, 2022 at 16:16
  • That's an HWIC. Also, there's no 15.x for the ancient 1700 line. (In fact, Cisco deleted the 1700's from history)
    – Ricky
    Jan 31, 2022 at 19:10

Does the router use the ARP table for the L2 switching (instead of MAC table as usually done on "regular" switch)?

No. The Etherswitch card is a layer 2 switch, and has most, if not all the features of a standalone switch. It forwards frames based on MAC addresses like any other switch.

  • then is there a way to show the card MAC table via the router IOS consoloe ? Jan 31, 2022 at 15:52

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