NETWORK ENGINEER STUFF: 2025

Saturday, 2 August 2025

Interview Questions & Answers for L1 Support Engineer

Section 1 - Desktop & Windows Troubleshooting

Q: How would you troubleshoot a slow or unresponsive Windows system?

✅Answer:

Check Task Manager for high CPU/RAM/disk usage.

Verify if unnecessary startup apps are running.

Run disk cleanup, remove temp files.

Check for Windows updates or driver issues.

Scan for malware/viruses.

If unresolved, consider restoring to a previous restore point or reimaging.

Q: What steps will you take to troubleshoot a Blue Screen of Death (BSOD)?

✅ Answer:

Note the error code (e.g., 0x0000007B).

Boot in Safe Mode to check recent driver/software changes.

Update or roll back drivers.

Check hardware (RAM/Hard disk) via diagnostics.

Run sfc /scannow and DISM commands.

Check Windows Event Viewer for logs.

Section 2 - Networking & IP

Q: How do you troubleshoot if a user cannot access the internet?

✅ Answer:

Verify physical connectivity (LAN/WiFi).

Check IP address via ipconfig.

Ping gateway & DNS.

Check DNS resolution by pinging websites (e.g., ping google.com).

Flush DNS (ipconfig /flushdns).

Restart NIC or renew IP (ipconfig /release & ipconfig /renew).

Verify firewall/proxy settings.

Q: Difference between DNS and DHCP?

✅ Answer:

DNS resolves hostnames to IP addresses.

DHCP automatically assigns IP addresses to devices in a network.

Q: How do you troubleshoot printer not working?

✅ Answer:

Check physical connections (USB/Network).

Verify if printer is online & default.

Restart spooler service (services.msc).

Update/reinstall printer drivers.

Test with another device.

Section 3 - Active Directory & O365

Q: What is Active Directory and why is it used?

✅ Answer:

A centralized directory service for managing users, computers, and permissions in a domain.

Used for authentication, authorization, and policy enforcement (via Group Policy).

Q: A user is unable to log into O365 – how would you troubleshoot?

✅ Answer:

Verify correct credentials & account status in Azure AD/Admin Portal.

Reset password if required.

Check internet and firewall/proxy settings.

Verify license assignment in O365 Admin.

Section 4 - SQL & WordPress (Basic)

Q: How do you connect to a SQL database and check connectivity?

✅ Answer:

Use SQL Server Management Studio (SSMS).

Test connection string (hostname/IP, username, password).

Ping database server or test via telnet <ip> 1433.

Q: What basic troubleshooting steps would you do for WordPress not loading?

✅ Answer:

Check if the web server (Apache/Nginx) is running.

Verify database connection in wp-config.php.

Clear browser cache and disable plugins.

Check domain DNS propagation.

Section 5 Behavioral & SLA-based Questions

Q: How do you handle an issue that you cannot resolve immediately?

✅ Answer:

Document steps tried.

Escalate to L2 team with logs/screenshots.

Keep user updated on SLA and resolution timeline.

Q: How do you prioritize multiple tickets?

✅ Answer:

Based on impact and urgency.

Critical business-impacting issues (server outage) first, then medium/low issues.

Follow ITIL guidelines if applicable.

Summary of L1 Support Engineer Role

Core Focus: First-level technical support (desktops, laptops, network basics, AD, O365).

Tasks: Troubleshoot user issues, maintain system health, escalate unresolved cases to L2/L3.

Tools Knowledge: AD, O365 admin portal, basic SQL, ticketing tools (e.g., ServiceNow), antivirus console.

Soft Skills: Client communication, vendor coordination, SLA adherence.

Tips to Ace the Interview

Brush up Basics:

IP addressing (private/public ranges), DNS/DHCP.

Windows troubleshooting commands (ping, ipconfig, netstat, nslookup).

Active Directory basics (adding/removing users).

Hands-On Practice:

Simulate printer setup, BSOD fixes in VM, create test O365 accounts (trial).

ITIL Awareness:

Know ticket priorities, escalation flow, SLA handling.

Communication Skills:

Explain technical fixes clearly to non-technical users.

Real Scenarios Prep:

Be ready for scenario-based Qs (e.g., "User can't access shared folder", "WiFi drops frequently").

Extra Edge:

Learn basic PowerShell commands, server patching, antivirus console basics.

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Thursday, 31 July 2025

Extended ACLs

An Extended Access Control List (ACL) allows you to filter traffic based on source IP, destination IP, protocol type (TCP, UDP, ICMP), source/destination port numbers.

+Numbered Extended ACL Ranges -

100–199

2000–2699

+ We can also use named ACLs

+ Placed close to Source - Since in extended ACLs we can filter on bases of Source IP , Destination IP ,port number so placing them near the source gives precise control over who can access what and how.

Lets block - port 80 http of server 20.1.1.1 for laptop 10.1.1.100

Source IP - 10.1.1.100

Destination IP - 20.1.1.1

Destination port number - 80

Step 1 - Creating Extended ACL

access-list 100 deny tcp 10.1.1.0 0.0.0.0 20.1.1.0 0.0.0.0 eq 80

access-list 100 permit ip any any

Router#show ip access-lists

Extended IP access list 100

10 deny tcp 10.1.1.0 0.0.0.0 20.1.1.0 0.0.0.0 eq www

20 permit ip any any

Step 2 - Apply the Extended ACL

We would need to apply it close to the source and that will be in in direction

interface GigabitEthernet0/0/0

ip access-group 100 in

Lets try from laptop to access port 80 and port 443 of server 20.1.1.100

Port 80 is not accessible

Port 443 is accessible

Now check the hits on the acl entry

Router#show ip access-lists

Extended IP access list 100

10 deny tcp 10.1.1.0 0.0.0.0 20.1.1.0 0.0.0.0 eq www (36 match(es))

20 permit ip any any

============================================

Complete configuration Router -

Router#show run

Building configuration...

Current configuration : 854 bytes

version 15.4

no service timestamps log datetime msec

no service timestamps debug datetime msec

no service password-encryption

hostname Router

ip cef

no ipv6 cef

spanning-tree mode pvst

interface GigabitEthernet0/0/0

ip address 10.1.1.1 255.255.255.0

ip access-group 100 in

duplex auto

speed auto

interface GigabitEthernet0/0/1

ip address 20.1.1.1 255.255.255.0

duplex auto

speed auto

interface GigabitEthernet0/0/2

no ip address

duplex auto

speed auto

shutdown

interface Vlan1

no ip address

shutdown

ip classless

ip flow-export version 9

access-list 100 deny tcp 10.1.1.0 0.0.0.0 20.1.1.0 0.0.0.0 eq www

access-list 100 permit ip any any

line con 0

line aux 0

line vty 0 4

end

Happy Learning !!

Network Engineer Stuff

Standard ACL

A Standard Access List Control ACL is a type of ACL used on Cisco

devices to filter network traffic based only on "Source IP Address"

>Match only SIP and cannot filter by DIP , ports or protocols

>Uses numbered ACL (1-99 and 1300 -1999) or named ACL .

> Applied as close to the destination

Configuration on Router

Step 1 - Configuration of Standard ACL

access-list 10 deny host 10.1.1.100

access-list 10 permit any

Router#show ip access-lists

Standard IP access list 10

10 deny host 10.1.1.100

20 permit any

Step 2 - Apply the ACL on the interface close to the destination

interface GigabitEthernet0/0/1

ip access-group 10 out

Now lets access server 20.1.1.100 from the Laptop

We can see that laptop is not able to access the server

On Router we can see the hits as well.

Router#show ip access-lists

Standard IP access list 10

10 deny host 10.1.1.100 (4 match(es))

20 permit any

Complete Router Configuration

Router#show run

Building configuration...

Current configuration : 750 bytes

version 15.4

no service timestamps log datetime msec

no service timestamps debug datetime msec

no service password-encryption

hostname Router

ip cef

no ipv6 cef

spanning-tree mode pvst

interface GigabitEthernet0/0/0

ip address 10.1.1.1 255.255.255.0

duplex auto

speed auto

interface GigabitEthernet0/0/1

ip address 20.1.1.1 255.255.255.0

ip access-group 10 out

duplex auto

speed auto

interface GigabitEthernet0/0/2

no ip address

duplex auto

speed auto

shutdown

interface Vlan1

no ip address

shutdown

ip classless

ip flow-export version 9

access-list 10 deny host 10.1.1.100

access-list 10 permit any

line con 0

line aux 0

line vty 0 4

end

Happy Learning !!

Network Engineer Stuff

Saturday, 26 July 2025

BGP CHAPTER 24 Originator ID , Cluster ID & Cluster List

Loop Prevention in RR Setups -

iBGP loop prevention mechanism - Split Horizon Rule

Route learned from an iBGP neighbor cannot be forwarded to other iBGP neighbor.

RR violates this rule so …”introduces risk of loops”

Originator ID

The Originator ID is set by the route reflector

32-bit router ID of the original iBGP speaker that injected the route. For eg R1

Visible in Route Reflector environments

Prevents loops if route comes back to the originator

Cluster ID & Cluster List

Cluster ID is an unique ID assigned to each Route Reflector.

Cluster List is a list of all Cluster IDs the route has passed through

When an RR reflects a route, it adds its own Cluster ID to the Cluster List.

If a router sees its own Cluster ID in the Cluster List → loop detected → route discarded

Cluster 1

R1 , R2 - Client

R3 - Route Reflector

Cluster 2

R4 , R5 - Client

R6 - Route Reflector

BGP Neighborship

R1_Client>show ip bgp summary

BGP router identifier 1.1.1.1, local AS number 100

BGP table version is 1, main routing table version 1

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

3.3.3.3 4 100 7 7 1 0 0 00:03:31 0

R2_Client>show ip bgp summary

BGP router identifier 2.2.2.2, local AS number 100

BGP table version is 1, main routing table version 1

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

3.3.3.3 4 100 6 8 1 0 0 00:03:48 0

R2_Client>

R3_RR1#show ip bgp summary

BGP router identifier 3.3.3.3, local AS number 100

BGP table version is 1, main routing table version 1

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

1.1.1.1 4 100 11 11 1 0 0 00:06:41 0

2.2.2.2 4 100 10 8 1 0 0 00:06:13 0

6.6.6.6 4 100 4 4 1 0 0 00:00:08 0

R4_Client>show ip bgp summary

BGP router identifier 4.4.4.4, local AS number 100

BGP table version is 1, main routing table version 1

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

6.6.6.6 4 100 9 9 1 0 0 00:05:01 0

R5_Client>show ip bgp summary

BGP router identifier 5.5.5.5, local AS number 100

BGP table version is 1, main routing table version 1

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

6.6.6.6 4 100 9 9 1 0 0 00:05:20 0

R5_Client>

R6_RR2#show ip bgp summary

BGP router identifier 6.6.6.6, local AS number 100

BGP table version is 1, main routing table version 1

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

3.3.3.3 4 100 5 5 1 0 0 00:01:10 0

4.4.4.4 4 100 10 10 1 0 0 00:05:43 0

5.5.5.5 4 100 10 10 1 0 0 00:05:43 0

R6_RR2#

=============================================

Now lets advertise a network 100.1.1.1/32 from R1 in BGP

R1_Client(config)#int loopback 100

R1_Client(config-if)#ip address 100.1.1.1 255.255.255.255

R1_Client(config)#router bgp 100

R1_Client(config-router)#network 100.1.1.1 mask 255.255.255.255

R1_Client(config-router)#^Z

Lets check on its RR - R3

R3_RR1#show ip bgp 100.1.1.1/32

BGP routing table entry for 100.1.1.1/32, version 2

Paths: (1 available, best #1, table default)

Advertised to update-groups:

2 3

Refresh Epoch 1

Local, (Received from a RR-client)

1.1.1.1 (metric 11) from 1.1.1.1 (1.1.1.1)

Origin IGP, metric 0, localpref 100, valid, internal, best

rx pathid: 0, tx pathid: 0x0

Lets check on RR2 - R6

R6_RR2#show ip bgp 100.1.1.1/32

BGP routing table entry for 100.1.1.1/32, version 2

Paths: (1 available, best #1, table default)

Advertised to update-groups:

Refresh Epoch 1

Local

1.1.1.1 (metric 21) from 3.3.3.3 (3.3.3.3)

Origin IGP, metric 0, localpref 100, valid, internal, best

Originator: 1.1.1.1, Cluster list: 3.3.3.3 ----------> ORIGINATOR ID OF R1 CLUSTER ID OF RR1

rx pathid: 0, tx pathid: 0x0

Now lets check on R4

R4_Client>show ip bgp 100.1.1.1/32

BGP routing table entry for 100.1.1.1/32, version 2

Paths: (1 available, best #1, table default)

Not advertised to any peer

Refresh Epoch 1

Local

1.1.1.1 (metric 31) from 6.6.6.6 (6.6.6.6)

Origin IGP, metric 0, localpref 100, valid, internal, best

Originator: 1.1.1.1, Cluster list: 6.6.6.6, 3.3.3.3 ---> RR2 Cluster ID is also attached

rx pathid: 0, tx pathid: 0x0

R4_Client>

For complete configuration - mail me on networkengineerstuff.com

Tuesday, 22 July 2025

Troubleshooting EIGRP !!

1️⃣ Mismatched Autonomous System (AS) Numbers

Description: Both routers must be in the same EIGRP AS.

Fix:

router eigrp 100

2️⃣ Interface in the Wrong VRF

Description: If the interface is in a VRF and EIGRP isn’t running in that VRF, the neighbor won’t form.

Fix: Configure EIGRP under the correct VRF context.

3️⃣ Passive Interface Enabled on EIGRP-Connected Interface

Description: Passive interface disables EIGRP hello packets.

Fix:

router eigrp 100
 no passive-interface e1/0

4️⃣ MTU Mismatch

Description: EIGRP includes MTU in its hello packets. If received MTU is less than interface MTU, neighborship fails.

Fix: Ensure MTU matches on both sides of the WAN link.

5️⃣ K-Values Mismatch

Description: Routers with different metric calculation settings (K-values) will not form neighbors.

Fix:


router eigrp 100
 metric weights 0 1 0 1 0 0  ! default

Or:


default metric weights

6️⃣ Authentication Mismatch

Description: MD5 authentication must be enabled with same key-string on both routers.

Fix:


key chain AUTHKEY
 key 1
  key-string Cisco123
!
interface e1/0
 ip authentication mode eigrp 100 md5
 ip authentication key-chain eigrp 100 AUTHKEY

7️⃣ Interface Not in the `network` Command

Description: If the interface is not covered by the network command, EIGRP won’t operate on it.

Fix:


router eigrp 100
 network 12.1.1.0 0.0.0.3

8️⃣ Interface is Down or Administratively Shut

Description: Basic, but often overlooked — if the interface is down, EIGRP won’t send or receive hello packets.

Fix:


interface e1/0
 no shutdown

9️⃣ IP Address Misconfiguration

Description: Wrong IP address — routers are not in the same subnet.

Fix: Assign valid IPs in the same subnet on both sides.

🔟 Access Control List (ACL) Blocking EIGRP

Description: ACLs on the interface or VTY lines may block EIGRP traffic (uses IP protocol number 88).

Fix: Allow EIGRP in ACL:


permit eigrp any any

1️⃣1️⃣ Duplicate Router IDs

Description: Duplicate router IDs won’t stop neighbor formation, but can cause route instability or flapping.

Fix:


router eigrp 100
 eigrp router-id 1.1.1.1

Ensure unique router IDs.

1️⃣2️⃣ Hello/Hold Timer Mismatch (older IOS versions)

Description: If timers differ significantly, routers may not recognize each other as valid neighbors.

Fix:


interface e1/0
 ip hello-interval eigrp 100 5
 ip hold-time eigrp 100 15

Set consistently on both routers.

1️⃣3️⃣ Unidirectional Link (Physical/Cabling Issue)

Description: One router sends hellos, but the other can’t receive — often due to cable, NIC, or virtual lab misconfig.

Fix: Check cabling or rebuild link in virtual environments.

1️⃣4️⃣ EIGRP Not Enabled for IPv6

Description: For IPv6, you must use ipv6 router eigrp, and EIGRP is configured per interface, not via network.

Fix:


interface e1/0
 ipv6 eigrp 100

🧪 Verification Commands

Command	What It Shows
`show ip eigrp neighbors`	Neighbor status
`show ip protocols`	AS, timers, passive interfaces
`debug eigrp packets`	Hellos, updates, and errors
`debug eigrp neighbors`	Adjacency process
`show running-config`	Authentication, K-values, interfaces

Network Engineer Stuff

Saturday, 28 June 2025

BGP Chapter 23 - BGP Route Reflector

A small Recap of BGP Split Horizon Rule

Route learned from an iBGP neighbor cannot be forwarded to other iBGP neighbor.

iBGP loop prevention mechanism .

Solution for this are :-

1) Full Mesh iBGP

2) Route Reflector

3) Confederation

In this post we will focus on Route Reflector (RR)

RR – A router that reflects routes between iBGP peers.

Client - A router that peers with the RR.

Non-client - A normal iBGP peer of the RR.

Route Reflection Behavior

When a RR receives a route

R1_CLIENT#show ip bgp summary

BGP router identifier 121.121.121.121, local AS number 100

BGP table version is 3, main routing table version 3

3 network entries using 432 bytes of memory

3 path entries using 240 bytes of memory

3/2 BGP path/bestpath attribute entries using 408 bytes of memory

1 BGP AS-PATH entries using 24 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 1104 total bytes of memory

BGP activity 3/0 prefixes, 3/0 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

2.2.2.2 4 100 67 66 3 0 0 00:56:11 2

R1_CLIENT#

R1_CLIENT#show ip bgp

BGP table version is 3, local router ID is 121.121.121.121

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

*> 100.1.1.0/24 0.0.0.0 0 32768 i

*>i 100.2.1.0/24 2.2.2.2 0 100 0 i

* i 100.6.1.0/24 6.6.6.6 0 100 0 200 i

R2_RR#show ip bgp summary

BGP router identifier 2.2.2.2, local AS number 100

BGP table version is 7, main routing table version 7

6 network entries using 864 bytes of memory

6 path entries using 480 bytes of memory

3/3 BGP path/bestpath attribute entries using 408 bytes of memory

1 BGP AS-PATH entries using 24 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 1776 total bytes of memory

BGP activity 6/0 prefixes, 6/0 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

1.1.1.1 4 100 66 67 7 0 0 00:56:11 1

3.3.3.3 4 100 64 65 7 0 0 00:56:07 1

4.4.4.4 4 100 66 66 7 0 0 00:56:13 1

5.5.5.5 4 100 67 68 7 0 0 00:57:38 1

6.6.6.6 4 200 64 66 7 0 0 00:55:59 1

R2_RR#

R2_RR#show ip bgp

BGP table version is 7, local router ID is 2.2.2.2

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

*>i 100.1.1.0/24 1.1.1.1 0 100 0 i

*> 100.2.1.0/24 0.0.0.0 0 32768 i

*>i 100.3.1.0/24 3.3.3.3 0 100 0 i

*>i 100.4.1.0/24 4.4.4.4 0 100 0 i

*>i 100.5.1.0/24 5.5.5.5 0 100 0 i

*> 100.6.1.0/24 6.6.6.6 0 0 200 i

R3_CLIENT#show ip bgp summary

BGP router identifier 3.3.3.3, local AS number 100

BGP table version is 3, main routing table version 3

3 network entries using 432 bytes of memory

3 path entries using 240 bytes of memory

3/2 BGP path/bestpath attribute entries using 408 bytes of memory

1 BGP AS-PATH entries using 24 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 1104 total bytes of memory

BGP activity 3/0 prefixes, 3/0 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

2.2.2.2 4 100 65 64 3 0 0 00:56:07 2

R3_CLIENT#

R3_CLIENT#show ip bgp

BGP table version is 3, local router ID is 3.3.3.3

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

*>i 100.2.1.0/24 2.2.2.2 0 100 0 i

*> 100.3.1.0/24 0.0.0.0 0 32768 i

* i 100.6.1.0/24 6.6.6.6 0 100 0 200 i

R4_NON_CLIENT#show ip bgp summary

BGP router identifier 4.4.4.4, local AS number 100

BGP table version is 3, main routing table version 3

3 network entries using 432 bytes of memory

3 path entries using 240 bytes of memory

3/2 BGP path/bestpath attribute entries using 408 bytes of memory

1 BGP AS-PATH entries using 24 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 1104 total bytes of memory

BGP activity 3/0 prefixes, 3/0 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

2.2.2.2 4 100 66 66 3 0 0 00:56:14 2

R4_NON_CLIENT#

R4_NON_CLIENT#show ip bgp

BGP table version is 3, local router ID is 4.4.4.4

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

*>i 100.2.1.0/24 2.2.2.2 0 100 0 i

*> 100.4.1.0/24 0.0.0.0 0 32768 i

* i 100.6.1.0/24 6.6.6.6 0 100 0 200 i

R4_NON_CLIENT#

R5_NON_CLIENT#show ip bgp summary

BGP router identifier 5.5.5.5, local AS number 100

BGP table version is 3, main routing table version 3

3 network entries using 432 bytes of memory

3 path entries using 240 bytes of memory

3/2 BGP path/bestpath attribute entries using 408 bytes of memory

1 BGP AS-PATH entries using 24 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 1104 total bytes of memory

BGP activity 3/0 prefixes, 3/0 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

2.2.2.2 4 100 68 67 3 0 0 00:57:38 2

R5_NON_CLIENT#

R5_NON_CLIENT#show ip bgp

BGP table version is 3, local router ID is 5.5.5.5

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

*>i 100.2.1.0/24 2.2.2.2 0 100 0 i

*> 100.5.1.0/24 0.0.0.0 0 32768 i

* i 100.6.1.0/24 6.6.6.6 0 100 0 200 i

R6_eBGP#show ip bgp summary

BGP router identifier 6.6.6.6, local AS number 200

BGP table version is 7, main routing table version 7

6 network entries using 864 bytes of memory

6 path entries using 480 bytes of memory

3/3 BGP path/bestpath attribute entries using 408 bytes of memory

1 BGP AS-PATH entries using 24 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 1776 total bytes of memory

BGP activity 6/0 prefixes, 6/0 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

2.2.2.2 4 100 66 64 7 0 0 00:55:59 5

R6_eBGP#

R6_eBGP#show ip bgp

BGP table version is 7, local router ID is 6.6.6.6

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

*> 100.1.1.0/24 2.2.2.2 0 100 i

*> 100.2.1.0/24 2.2.2.2 0 0 100 i

*> 100.3.1.0/24 2.2.2.2 0 100 i

*> 100.4.1.0/24 2.2.2.2 0 100 i

*> 100.5.1.0/24 2.2.2.2 0 100 i

*> 100.6.1.0/24 0.0.0.0 0 32768 i

Now lets configure

R2 as RR making R1 and R3 as client

When we configure iBGP neighbor as route-reflector-client the BGP Session get flapped.

R2_RR(config)#router bgp 100

R2_RR(config-router)#neighbor 1.1.1.1 route-reflector-client

*Jun 28 12:37:29.943: %BGP-5-ADJCHANGE: neighbor 1.1.1.1 Down RR client config change

*Jun 28 12:37:29.943: %BGP_SESSION-5-ADJCHANGE: neighbor 1.1.1.1 IPv4 Unicast topology base removed from session RR client config change

*Jun 28 12:37:30.479: %BGP-5-ADJCHANGE: neighbor 1.1.1.1 Up

R2_RR(config-router)#

R2_RR(config-router)#neighbor 3.3.3.3 route-reflector-client

R2_RR(config-router)#

*Jun 28 12:37:41.615: %BGP-5-ADJCHANGE: neighbor 3.3.3.3 Down RR client config change

*Jun 28 12:37:41.615: %BGP_SESSION-5-ADJCHANGE: neighbor 3.3.3.3 IPv4 Unicast topology base removed from session RR client config change

*Jun 28 12:37:42.703: %BGP-5-ADJCHANGE: neighbor 3.3.3.3 Up

R2_RR(config-router)#^Z

R2_RR#

R1_CLIENT#show ip bgp

BGP table version is 8, local router ID is 121.121.121.121

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

*> 100.1.1.0/24 0.0.0.0 0 32768 i

*>i 100.2.1.0/24 2.2.2.2 0 100 0 i

*>i 100.3.1.0/24 3.3.3.3 0 100 0 i

* i 100.4.1.0/24 4.4.4.4 0 100 0 i

* i 100.5.1.0/24 5.5.5.5 0 100 0 i

* i 100.6.1.0/24 6.6.6.6 0 100 0 200 i

R3_CLIENT>show ip bgp

BGP table version is 8, local router ID is 3.3.3.3

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

*>i 100.1.1.0/24 1.1.1.1 0 100 0 i

*>i 100.2.1.0/24 2.2.2.2 0 100 0 i

*> 100.3.1.0/24 0.0.0.0 0 32768 i

* i 100.4.1.0/24 4.4.4.4 0 100 0 i

* i 100.5.1.0/24 5.5.5.5 0 100 0 i

* i 100.6.1.0/24 6.6.6.6 0 100 0 200 i

R4_NON_CLIENT>show ip bgp

BGP table version is 3, local router ID is 4.4.4.4

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

* i 100.1.1.0/24 1.1.1.1 0 100 0 i

*>i 100.2.1.0/24 2.2.2.2 0 100 0 i

* i 100.3.1.0/24 3.3.3.3 0 100 0 i

*> 100.4.1.0/24 0.0.0.0 0 32768 i

* i 100.6.1.0/24 6.6.6.6 0 100 0 200 i

R5_NON_CLIENT#show ip bgp

BGP table version is 3, local router ID is 5.5.5.5

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

* i 100.1.1.0/24 1.1.1.1 0 100 0 i

*>i 100.2.1.0/24 2.2.2.2 0 100 0 i

* i 100.3.1.0/24 3.3.3.3 0 100 0 i

*> 100.5.1.0/24 0.0.0.0 0 32768 i

* i 100.6.1.0/24 6.6.6.6 0 100 0 200 i

Thanks for Reading !!

Network Engineer Stuff

Pages

Saturday, 2 August 2025

Interview Questions & Answers for L1 Support Engineer

Thursday, 31 July 2025

Extended ACLs

Standard ACL

Saturday, 26 July 2025

BGP CHAPTER 24 Originator ID , Cluster ID & Cluster List

Tuesday, 22 July 2025

Troubleshooting EIGRP !!

1️⃣ Mismatched Autonomous System (AS) Numbers

2️⃣ Interface in the Wrong VRF

3️⃣ Passive Interface Enabled on EIGRP-Connected Interface

4️⃣ MTU Mismatch

5️⃣ K-Values Mismatch

6️⃣ Authentication Mismatch

7️⃣ Interface Not in the network Command

8️⃣ Interface is Down or Administratively Shut

9️⃣ IP Address Misconfiguration

🔟 Access Control List (ACL) Blocking EIGRP

1️⃣1️⃣ Duplicate Router IDs

1️⃣2️⃣ Hello/Hold Timer Mismatch (older IOS versions)

1️⃣3️⃣ Unidirectional Link (Physical/Cabling Issue)

1️⃣4️⃣ EIGRP Not Enabled for IPv6

🧪 Verification Commands

Saturday, 28 June 2025

BGP Chapter 23 - BGP Route Reflector

7️⃣ Interface Not in the `network` Command