1

This is almost the same question as How to setup port forwarding on Cisco Router running Version 15.2(4)M6. The problem is that the command used in the answer is not available:

ip nat inside source static tcp 172.29.1.130 25565 5.6.7.8 25565

This happens when I try the same thing

Cisco(config)#ip nat inside source static
                                   ^
% Invalid input detected at '^' marker.

Cisco(config)#ip nat inside source ?
  list  Specify access list describing local addresses

Cisco(config)#

The only valid input accepted after source is an access list, not static. I am running this on a Catalyst WS-C3750X-48PF-S with ios 15.2(4)E10 (c3750e-universalk9-mz.152-4.E10.bin). Is this feature not available for this switch? Or is there another way of accomplishing the same goal?

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  • 1
    Cisco does not do NAT on switches because it claims that it is so resource intensive that it requires dedicated hardware, which is only found on Cisco routers.
    – Ron Maupin
    Sep 26 '20 at 0:24
  • @RonMaupin Thanks, I just now found that out elsewhere. Seems a silly limitation to me. I guess I'll have to put a Mikrotik router in front to handle the WAN/NAT.
    – ahab
    Sep 26 '20 at 0:30
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer.
    – Ron Maupin
    Dec 16 '20 at 23:29
3

Cisco catalyst 3750 is layer3 switch where NAT features is not available in this switch . Cisco developed layer3 switches to run only with limited features of layer3 stacks . NAT is not feasible in layer3 switch this is the reason NAT policy is not recognised by cisco 3750 layer3 switch .

Cisco layer3 switch can provide fallowing feature

  1. DHCP
  2. Routing
  3. access-list Configuration
  4. private Vlan 5)inter-Vlan routing (SVI) Configuration
  5. can have layer2 features as well.
0

After I found the right search engine query, I discovered that it seems full NAT support (including this feature) is not available on Layer 3 switches until 6500. What a shame, even when the switch was released this was a popular feature and the switch is certainly capable of doing this if it were allowed by the software.

6
  • I guess you really do not understand how resource intensive NAT is. Each of the three supported protocols (TCP, UDP, and ICMP) needs it own NAT table, and it requires a lot of CPU time. Switches are designed to switch at wirespeed because switching is done in hardware, so the switch CPU and RAM are limited compared to routers. Cisco adds special hardware to routers to assist with NAT. putting that in switches requires more than a software change, it requires a beefier CPU and more RAM, too.
    – Ron Maupin
    Sep 26 '20 at 0:34
  • In any case, NAT is not a common use inside a business network, where things are either routed or switched on the business network. NAT should only be used when absolutely necessary (private to public addressing, or overlapping addressing where it should be a temporary solution until the overlapping addressing can be resolved). Within a business, where switches are, the use case for NAT is very, very limited.
    – Ron Maupin
    Sep 26 '20 at 0:37
  • I guess I did underestimate that. Cisco wasn't really marketing these switches to small businesses (who might have 20-50 hosts and wouldn't want or need two "boxes") at the time. In my defense, a lowly Linksys WRT54G (with 1/8 of the RAM) can do this, but I suppose it's my fault for mistaking a L3 switch for a router and think they more or less had the same basic capabilities. It would be nice if Cisco had an easy way to check what their past products were capable of.
    – ahab
    Sep 26 '20 at 1:00
  • The Linksys is very limited in the NAT tables, and the NAT does slow networking, but you usually do not see that because the WAN speed is so much slower than the LAN speed, not suitable for a real business network. I see questions on Super User where people are complaining that their home routers top out at 20 or 30 active devices and NAT.
    – Ron Maupin
    Sep 26 '20 at 1:05
  • Also, routing within a business usually requires routing protocols (RAM and CPU) to share routing information among the business routers, and much larger routing tables (more RAM) than a home network device that really has a single static, default route from the LAN to the WAN, and no real need for routing protocols.
    – Ron Maupin
    Sep 26 '20 at 1:10

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