Les adresses IP ne peuvent pas être configurées sur des liaisons L2.

Hello

On this range of routers, you cannot directly configure an address on a fastethernet port.
In fact, the FA0-FA03 ports are like a switch.

You need to create VLANs, assign an address to the VLAN, and assign the port to the VLAN.

See examples here

--
"To fix something that doesn't work or makes too much noise, you just need to hit it with something that works better or makes more noise." Les Shadoks

What IOS is used?

Advanced IP Services is required to support multiple VLANs.
Advanced Security does not support them...

--
"To fix something that isn't working or is too noisy, you just need to hit it with something that works better or makes more noise" The Shadoks

How can I find out? It's a Cisco 878.

When I run a show configuration, I get this (I don't know if it helps you):

router2#show configuration
Using 3060 out of 131072 bytes
!
version 12.4
no service pad
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname router2
!
boot-start-marker
boot-end-marker
!
logging buffered 51200 warnings
!
no aaa new-model
!
resource policy
!
ip subnet-zero
ip cef
no ip dhcp use vrf connected
ip dhcp excluded-address 10.10.10.1
!
ip dhcp pool sdm-pool
import all
network 10.10.10.0 255.255.255.248
default-router 10.10.10.1
lease 0 2
!
!
no ip domain lookup
ip domain name yourdomain.com
!
!
crypto pki trustpoint TP-self-signed-319006384
enrollment selfsigned
subject-name cn=IOS-Self-Signed-Certificate-319006384
revocation-check none
rsakeypair TP-self-signed-319006384
!
!
crypto pki certificate chain TP-self-signed-319006384
certificate self-signed 01 nvram:IOS-Self-Sig#3401.cer
username cisco privilege 15 secret 5 $1$HyHw$/olHc8OFKMAm4IK8PPXZC/
!
!
controller DSL 0
line-term cpe
!
!
crypto isakmp policy 100
encr aes
group 2
crypto isakmp key VpnK3! address 10.10.10.1
!
!
crypto ipsec transform-set IPSECSET esp-aes esp-sha-hmac
!
crypto map IPSECMAP 100 ipsec-isakmp
set peer 10.10.10.1
set transform-set IPSECSET
match address CRYPTOACL
!
!
!
interface BRI0
no ip address
encapsulation hdlc
shutdown
!
interface FastEthernet0
!
interface FastEthernet1
!
interface FastEthernet2
!
interface FastEthernet3
!
interface Vlan1
description $ETH-SW-LAUNCH$$INTF-INFO-HWIC 4ESW$
ip address 10.10.10.2 255.0.0.0
ip access-group IPSECACL out
ip tcp adjust-mss 1452
crypto map IPSECMAP
!
ip classless
!
ip http server
ip http access-class 23
ip http authentication local
ip http secure-server
ip http timeout-policy idle 60 life 86400 requests 10000
!
ip access-list extended CRYPTOACL
permit ip 10.10.10.0 0.0.0.255 10.10.10.0 0.0.0.255
ip access-list extended IPSECACL
permit ahp host 10.10.10.2 host 10.10.10.1
permit esp host 10.10.10.2 host 10.10.10.1
permit udp host 10.10.10.2 host 10.10.10.1 eq isakmp
!
access-list 23 permit 10.10.10.0 0.0.0.7
no cdp run
!
control-plane
!
banner login ^C
-----------------------------------------------------------------------
Cisco Router and Security Device Manager (SDM) is installed on this device.
This feature requires the one-time use of the username "cisco"
with the password "cisco". The default username and password have a privilege level of 15.

Please change these publicly known initial credentials using SDM or the IOS CLI.
Here are the Cisco IOS commands.

username <myuser> privilege 15 secret 0 <mypassword>
no username cisco

Replace <myuser> and <mypassword> with the username and password you want to use.

For more information about SDM please follow the instructions in the QUICK START
GUIDE for your router or go to https://www.cisco.com/c/en/us/products/cloud-systems-management/managed-services-accelerator/index.html
-----------------------------------------------------------------------
^C
!
line con 0
login local
no modem enable
speed 115200
line aux 0
line vty 0 4
access-class 23 in
privilege level 15
login local
transport input telnet ssh
!
scheduler max-task-time 5000
end