how to configured two routers cisco 1841 ACL LIST with steps

 how to configured two routers cisco 1841 ACL LIST with steps

Here is a basic step-by-step configuration for two Cisco 1841 Integrated Services Router routers using:

• Static IP addressing

• Serial connection

• ACL (Access Control List)

• Routing between two LAN networks

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Network Topology

PC1 ---- Router1 ===== Router2 ---- PC2
        Fa0/0   Serial   Fa0/0

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IP Addressing Table

Device	Interface	IP Address	Subnet Mask
Router1	Fa0/0	192.168.1.1	255.255.255.0
Router1	S0/0/0	10.0.0.1	255.255.255.252
Router2	S0/0/0	10.0.0.2	255.255.255.252
Router2	Fa0/0	192.168.2.1	255.255.255.0
PC1	NIC	192.168.1.10	255.255.255.0
PC2	NIC	192.168.2.10	255.255.255.0

Gateway:

• PC1 → 192.168.1.1

• PC2 → 192.168.2.1

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Step 1: Connect Routers

Use:

• Console cable for configuration

• Serial DCE/DTE cable between routers

• Ethernet cable to PCs

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Step 2: Configure Router1

Enter privileged mode:

enable
configure terminal

Configure FastEthernet

interface fa0/0
ip address 192.168.1.1 255.255.255.0
no shutdown
exit

Configure Serial Interface

interface s0/0/0
ip address 10.0.0.1 255.255.255.252
clock rate 64000
no shutdown
exit

Configure Static Route

ip route 192.168.2.0 255.255.255.0 10.0.0.2

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Step 3: Configure Router2

enable
configure terminal

Configure FastEthernet

interface fa0/0
ip address 192.168.2.1 255.255.255.0
no shutdown
exit

Configure Serial Interface

interface s0/0/0
ip address 10.0.0.2 255.255.255.252
no shutdown
exit

Configure Static Route

ip route 192.168.1.0 255.255.255.0 10.0.0.1

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Step 4: Configure ACL on Router1

Example:
Block PC1 from accessing Router2 LAN.

Create Standard ACL

access-list 10 deny 192.168.1.10
access-list 10 permit any

Apply ACL to Interface

interface s0/0/0
ip access-group 10 out
exit

This ACL:

• Denies PC1 (192.168.1.10)

• Allows all other traffic

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Step 5: Save Configuration

On both routers:

copy running-config startup-config

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Step 6: Verify Configuration

Check Interfaces

show ip interface brief

Check Routing Table

show ip route

Check ACL

show access-lists

Test Connectivity

From PC1:

ping 192.168.2.10

If ACL is working:

• PC1 ping fails

• Other PCs can communicate

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Example Extended ACL

To block only Telnet traffic:

access-list 101 deny tcp 192.168.1.0 0.0.0.255 192.168.2.0 0.0.0.255 eq 23
access-list 101 permit ip any any

Apply:

interface s0/0/0
ip access-group 101 out

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Useful Commands

Command	Purpose
show running-config	View current config
show ip route	View routes
show access-lists	View ACL rules
ping	Test network
traceroute	Trace route

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Important Notes

• Use clock rate 64000 only on DCE side.

• Use no shutdown on all interfaces.

• ACL rules are processed top to bottom.

• Standard ACL filters source IP only.

• Extended ACL filters protocol, source, and destination.

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Cisco ACL Logic

deny → block traffic
permit → allow traffic

Example formula:

192.168.1.0/24 \rightarrow \text{deny or permit traffic}

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