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eBGP with a password, and an inbound prefix-list
Enterprise Advanced 2 devices 5 checked tasks 100 points Plan lab
Peer with the provider the way you would in production: a TCP MD5 password on the session, and an inbound prefix-list that accepts only the prefixes you expect — here the provider offers three networks and you must refuse the one that is not theirs to sell. You build it in a browser, type real commands at each device, and every task below is
checked against the running configuration — so you find out it is wrong before anybody else does.
Open this lab in the simulator
The simulator runs in your browser with nothing to install. This lab is part of the full simulator: open it free for 7 days with a new account, then with a plan. It needs an account, which keeps your progress.
The scenario
Peer with the provider the way you would in production: a TCP MD5 password on the session, and an inbound prefix-list that accepts only the prefixes you expect — here the provider offers three networks and you must refuse the one that is not theirs to sell.
Your role: a network engineer on the enterprise team. Level: Advanced Done when: all 5 goals show as passed (100 points).
Network status
Devices: 2 routers, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. Customer starts with addresses (G0/1 203.0.113.1/30, L0 192.0.2.1/24) and BGP 65001 already configured. Provider starts with addresses (G0/0/1 203.0.113.2/30, L1 198.51.100.1/24, L2 198.51.101.1/24, L3 10.99.0.1/24) and BGP 65002 already configured. Known problems
The network worked and now does not: the scenario above says what users report. The cause is a configuration fault, not a cable. Find it with show commands (interfaces, routes, neighbours, running-config) before you change anything; fix only what is wrong. Goals
The session to the provider carries a password (20 pts) The eBGP session is Established (30 pts) A prefix-list is applied inbound to the neighbour (20 pts) The legitimate prefix 198.51.100.0/24 is accepted (15 pts) The private 10.99.0.0/24 the provider should not be selling is refused (15 pts) The activity, in order
The session to the provider carries a password Why: This is the task that checks your configuration directly: the line must really be there, not just look right. Verify with: show running-config The eBGP session is Established Why: BGP does nothing until the TCP session is Established. Active or Idle means a wrong AS number, no route to the peer, or a block. Verify with: show ip bgp summary A prefix-list is applied inbound to the neighbour Why: This is the task that checks your configuration directly: the line must really be there, not just look right. Verify with: show running-config The legitimate prefix 198.51.100.0/24 is accepted Why: BGP only advertises what you tell it to AND what is in the routing table. Verify with: show ip bgp The private 10.99.0.0/24 the provider should not be selling is refused Why: Reading a show command is the core skill of troubleshooting: the output is the truth, not your configuration. Verify with: show ip bgp Tips
Work in the order given: later goals depend on the earlier ones. After every change, run the verify command before moving on; do not guess. Stuck? Read the verify output first. It names the interface, neighbour or route that is wrong. Common mistake: Password on one side only (the session never comes up) Common mistake: A prefix-list with no permit at the end (implicit deny drops everything) Common mistake: Filtering in the wrong direction Why this matters
Never accept from a peer everything it offers. A TCP MD5 password protects the session; an inbound prefix-list protects the table. A provider that leaks a private or foreign prefix must not be able to put it in your routing table.
What you will be able to do
Configure an eBGP session with a password
Write and apply an inbound prefix-list
Verify accepted and refused prefixes in show ip bgp
The network
ISR 2911, ISR 4331 — 2 devices in all, already cabled.
Gi0/1 203.0.113.1/30 Gi0/0/1 203.0.113.2/30 Customer Provider Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
Customer ISR 2911 configure it Provider ISR 4331 configure it
Cabling
Customer Gi0/1 ↔ Provider Gi0/0/1
What is configured at the start
These are already configured when the lab opens — including, where this is a troubleshooting lab, the fault itself:
Customer interface g0/1
ip address 203.0.113.1 255.255.255.252
no shutdown
exit
interface lo0
ip address 192.0.2.1 255.255.255.0
no shutdown
exit
router bgp 65001
bgp router-id 1.1.1.1
network 192.0.2.0 mask 255.255.255.0 Provider interface g0/0/1
ip address 203.0.113.2 255.255.255.252
no shutdown
exit
interface lo1
ip address 198.51.100.1 255.255.255.0
no shutdown
exit
interface lo2
ip address 198.51.101.1 255.255.255.0
no shutdown
exit
interface lo3
ip address 10.99.0.1 255.255.255.0
no shutdown
exit
router bgp 65002
bgp router-id 2.2.2.2
neighbor 203.0.113.1 remote-as 65001
neighbor 203.0.113.1 password B6P-S3cret
network 198.51.100.0 mask 255.255.255.0
network 198.51.101.0 mask 255.255.255.0
network 10.99.0.0 mask 255.255.255.0 Tasks, and how each one is checked
Every task is decided by reading the live network — a neighbour in FULL, a ping that succeeds, a line in the running configuration — not by looking for a keyword you typed. The same command shows you what the lab sees.
# Task Pts How to verify it yourself
1 The session to the provider carries a password 20 On Customer: show running-config contains the line(s) matching neighbor 203\.0\.113\.2 password. 2 The eBGP session is Established 30 On Customer: show ip bgp summary — neighbour 203.0.113.2 is Established. 3 A prefix-list is applied inbound to the neighbour 20 On Customer: show running-config contains the line(s) matching neighbor 203\.0\.113\.2 prefix-list \S+ in. 4 The legitimate prefix 198.51.100.0/24 is accepted 15 On Customer: show ip bgp lists 198.51.100.0/24. 5 The private 10.99.0.0/24 the provider should not be selling is refused 15 On Customer: show ip bgp output matches 10\.99\.0\.0 — it must not .
Stuck? Ask the coach
Tell the coach what you see or what you tried. It gives you a hint, not the answer, the way a senior engineer would. Included with a free trial or any plan.
Ask the coach
Common mistakes
Password on one side only (the session never comes up)
A prefix-list with no permit at the end (implicit deny drops everything)
Filtering in the wrong direction
Reference solution
Try it yourself first — the lab checks your work either way. This is one configuration that makes every task pass, device by device:
Customer ip prefix-list FROM-ISP seq 10 deny 10.0.0.0/8 le 32
ip prefix-list FROM-ISP seq 20 permit 0.0.0.0/0 le 24
router bgp 65001
neighbor 203.0.113.2 remote-as 65002
neighbor 203.0.113.2 password B6P-S3cret
neighbor 203.0.113.2 prefix-list FROM-ISP in
exit Where this is examined
CCNP ENARSI (BGP), CCIE EI (BGP policy), CCNP SP.
This lab practises these topics in the zNetLaB certification courses:
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