01-01-2008 06:25 PM - edited 03-12-2019 05:56 PM
When you have two nat
1)nat (xxxx) 1 access-list xxxx
GLOBAL (yyyy) 1 193.243.64.227
access-list xxxx permit ip host 10.80.133.1 any
2)nat (xxxx)0 0.0.0.0 0.0.0.0
access-list xxxx permit ip host 10.80.133.1 any
whcih will taker precedence?
01-01-2008 07:15 PM
Hi Aksher
You have never rated the useful posts of experts here. Please rate useful. You have NEVER! rated. Please show respect. Rating a post does not cost any fee.
Regards
01-01-2008 09:16 PM
Agree.. we are all always in the look to help out others, in return it is good to use the rating system which in fact helps netpros to improve even more in assisting others.
01-01-2008 09:46 PM
Aksher,
Here is the order of operations for NAT on the firewall:
1. nat 0 access-list (nat-exempt)
2. Match existing xlates
3. Match static commands
a. Static NAT with and without access-list
b. Static PAT with and without access-list
4. Match nat commands
a. nat [id] access-list (first match)
b. nat [id] [address] [mask] (best match)
i. If the ID is 0, create an identity xlate
ii. Use global pool for dynamic NAT
iii. Use global pool for dynamic PAT
Be aware that in your second example, you are not referencing the ACL listed directly below it. The space inside the parenthesis is used to reference an interface. (2 would fall in to the OoO 4bi and 1) would fall in to the OoO 4a
Thanks,
-=Blayne
01-01-2008 10:40 PM
In 2, when you say "Match existing xlates" does it mean the existing xlates pertaining to 1
01-02-2008 06:16 AM
It means any existing xlate currently in the xlate table.
eg.
You have the following command in your config:
static (inside,outside) 87.45.29.48 192.168.1.1 netmask 255.255.255.255
You build an xlate with this static. You then experience traffic that would use this same static, but you didn't check the xlate table. - Problem!
So you should always check to see if an xlate exists in the table before attempting to create a translation based on a NAT rule.
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