NETWORK LESSON

Network Engineers Guide to IS-IS – Part 2

Published by

Recto Orpia

on

This is the second part of my IS-IS routing protocol post. I’m adding  Level-2 router on my IS-IS routing domain to explore further on how IS-IS protocol works.

Some key pointers to take note on the difference of the routes received by a Level-1 router and Level-2 router:
  • Level-1 router will not be able received any prefix advertised by another Level-1 router from another area but rather it will inject a default route to reach that prefix.
  • Once a level 1-2 router is connected to another area, it will set a special bit in its level 1 LSP called the attached bit. 
  • When a level 1 router sees the attached bit, it will generate a default route that is pointed to the level 1-2 router.
  • Level-2 router will received all the prefix that are advertised into IS-IS from both a Level-1, Level-2 routers or from Level 1-2 routers.  This prefix will be marked as L2 or IS-IS Level 2 routes.

Considerations:
AFI is set to 49
System ID will be 0000.0000.000X where X is the router number.

Legend:
R1 – Level 1 router
R2 – Level 1-2 router
R3 – Level 1-2 router
R4 – Level 1 router
R5 – Level 2 router

 R1:

interface Loopback1
 ip address 10.10.10.10 255.255.255.255
 ip router isis
!
interface GigabitEthernet2/0
 ip address 172.16.12.1 255.255.255.0
 ip router isis
 negotiation auto
!
router isis
 net 49.0012.0000.0000.0001.00
 is-type level-1

IS-IS Neighbors status:

R1#show isis neighbors

System Id      Type Interface   IP Address      State Holdtime Circuit Id
R2             L1   Gi2/0       172.16.12.2     UP    9        R2.01

R1#

LSP Database

R1#show isis database verbose

IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime      ATT/P/OL
R1.00-00            * 0x0000000B   0x51F1        597               0/0/0
  Area Address: 49.0012
  NLPID:        0xCC
  Hostname: R1
  IP Address:   10.10.10.10
  Metric: 10         IP 172.16.12.0 255.255.255.0
  Metric: 10         IP 10.10.10.10 255.255.255.255
  Metric: 10         IS R2.01
R2.00-00              0x0000000B   0x1665        572               1/0/0
  Area Address: 49.0012
  NLPID:        0xCC
  Hostname: R2
  IP Address:   20.20.20.20
  Metric: 10         IP 172.16.12.0 255.255.255.0
  Metric: 10         IP 20.20.20.20 255.255.255.255
  Metric: 10         IP 172.16.23.0 255.255.255.0
  Metric: 10         IS R2.01
R2.01-00              0x00000007   0x72D8        930               0/0/0
  Metric: 0          IS R2.00
  Metric: 0          IS R1.00


 Tips:
  • R1 have only the Level-1 LSP details with all its connected interface and also from R2. 
  • No other prefix learned by R1.

 R1#show ip route isis

Codes: L – local, C – connected, S – static, R – RIP, M – mobile, B – BGP
       D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
       N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
       E1 – OSPF external type 1, E2 – OSPF external type 2
       i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
       ia – IS-IS inter area, * – candidate default, U – per-user static route
       o – ODR, P – periodic downloaded static route, H – NHRP, l – LISP
       + – replicated route, % – next hop override

Gateway of last resort is 172.16.12.2 to network 0.0.0.0

i*L1  0.0.0.0/0 [115/10] via 172.16.12.2, 00:48:19, GigabitEthernet2/0
      20.0.0.0/32 is subnetted, 1 subnets
i L1     20.20.20.20 [115/20] via 172.16.12.2, 01:26:24, GigabitEthernet2/0
      172.16.0.0/16 is variably subnetted, 3 subnets, 2 masks
i L1     172.16.23.0/24 [115/20] via 172.16.12.2, 01:23:42, GigabitEthernet2/0
R1# 

 Tips:
  • As seen above, R1 have injected a default route via R2. This is true as Level-1 routers will not learned the specific prefix from other Areas but rather it only learned about the Prefix on its area where it belongs to.


     Let’s have a look on R2 configurations:

    interface Loopback2
     ip address 20.20.20.20 255.255.255.255
     ip router isis
    !
    interface GigabitEthernet1/0
     ip address 172.16.23.2 255.255.255.0
     ip router isis
     negotiation auto
    !
    interface GigabitEthernet2/0
     ip address 172.16.12.2 255.255.255.0
     ip router isis
     negotiation auto
    !
    router isis
     net 49.0012.0000.0000.0002.00

     IS-IS neighbors:

    R2#show isis neighbors

    System Id      Type Interface   IP Address      State Holdtime Circuit Id
    R1             L1   Gi2/0       172.16.12.1     UP    27       R2.01
    R3             L2   Gi1/0       172.16.23.3     UP    9        R3.03

    R2#

    Since R2 is a Level 1-2 router, it has the LSP for both Level-1 and Level-2 routers.

    R2#show isis database verbose

    IS-IS Level-1 Link State Database:
    LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime      ATT/P/OL
    R1.00-00              0x0000000C   0x4FF2        647               0/0/0
      Area Address: 49.0012
      NLPID:        0xCC
      Hostname: R1
      IP Address:   10.10.10.10
      Metric: 10         IP 172.16.12.0 255.255.255.0
      Metric: 10         IP 10.10.10.10 255.255.255.255
      Metric: 10         IS R2.01
    R2.00-00            * 0x0000000C   0x1466        670               1/0/0
      Area Address: 49.0012
      NLPID:        0xCC
      Hostname: R2
      IP Address:   20.20.20.20
      Metric: 10         IP 172.16.12.0 255.255.255.0
      Metric: 10         IP 20.20.20.20 255.255.255.255
      Metric: 10         IP 172.16.23.0 255.255.255.0
      Metric: 10         IS R2.01
    R2.01-00            * 0x00000008   0x70D9        1086              0/0/0
      Metric: 0          IS R2.00
      Metric: 0          IS R1.00
    IS-IS Level-2 Link State Database:
    LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime      ATT/P/OL
    R2.00-00            * 0x0000000C   0x6B4A        938               0/0/0
      Area Address: 49.0012
      NLPID:        0xCC
      Hostname: R2
      IP Address:   20.20.20.20
      Metric: 10         IS R3.03
      Metric: 20         IP 10.10.10.10 255.255.255.255
      Metric: 10         IP 20.20.20.20 255.255.255.255
      Metric: 10         IP 172.16.12.0 255.255.255.0
      Metric: 10         IP 172.16.23.0 255.255.255.0
    R3.00-00              0x0000000C   0x5D61        758               0/0/0
      Area Address: 49.0034
      Area Address: 49.0035
      NLPID:        0xCC
      Hostname: R3
      IP Address:   172.16.35.3
      Metric: 10         IS R3.03
      Metric: 10         IS R5.01
      Metric: 20         IP 40.40.40.40 255.255.255.255
      Metric: 10         IP 172.16.23.0 255.255.255.0
      Metric: 10         IP 172.16.34.0 255.255.255.0
      Metric: 10         IP 172.16.35.0 255.255.255.0
    R3.03-00              0x00000005   0x17B9        905               0/0/0
      Metric: 0          IS R3.00
      Metric: 0          IS R2.00
    R5.00-00              0x00000008   0x6F4E        603               0/0/0
      Area Address: 49.0035
      NLPID:        0xCC
      Hostname: R5
      IP Address:   50.50.50.50
      Metric: 10         IS R5.01
      Metric: 10         IP 50.50.50.50 255.255.255.255
      Metric: 10         IP 172.16.35.0 255.255.255.0
    R5.01-00              0x00000005   0x4A83        480               0/0/0
      Metric: 0          IS R5.00
      Metric: 0          IS R3.00
    R2#


     Few things to note on the routing table on R2:
    • The prefix 40.40.40.40/32 is advertised by a R4 which is a Level-1 router but R2 is receiving this prefix as Level-2 routes. 
    • This is because the Level 1-2 router on Area 34 have copied the LSP from its Level-1 LSP database to its Level-2 LSP database and have it advertised on R2 as both are backbone routers.
    • We have to take note of the Administrative distance of IS-IS which is 115 and the cumulative cost is based on a per hops. The cost per hop is 10 irregardless of the bandwidth. So in the case of 40.40.40.40/32, the total cost to reach this prefix from R2 is 30.
    • We can also see the prefix 10.0.0.0/32 as L1 with a cost of 20.

    R2#show ip route isis
    Codes: L – local, C – connected, S – static, R – RIP, M – mobile, B – BGP
           D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
           N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
           E1 – OSPF external type 1, E2 – OSPF external type 2
           i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
           ia – IS-IS inter area, * – candidate default, U – per-user static route
           o – ODR, P – periodic downloaded static route, H – NHRP, l – LISP
           + – replicated route, % – next hop override

    Gateway of last resort is not set

          10.0.0.0/32 is subnetted, 1 subnets
    i L1     10.10.10.10 [115/20] via 172.16.12.1, 01:39:01, GigabitEthernet2/0
          40.0.0.0/32 is subnetted, 1 subnets
    i L2     40.40.40.40 [115/30] via 172.16.23.3, 01:00:56, GigabitEthernet1/0
          50.0.0.0/32 is subnetted, 1 subnets
    i L2     50.50.50.50 [115/30] via 172.16.23.3, 01:00:47, GigabitEthernet1/0
          172.16.0.0/16 is variably subnetted, 6 subnets, 2 masks
    i L2     172.16.34.0/24 [115/20] via 172.16.23.3, 01:00:56, GigabitEthernet1/0
    i L2     172.16.35.0/24 [115/20] via 172.16.23.3, 01:00:56, GigabitEthernet1/0

    R2#

    Looking at R3, 3 neighbors were formed :

    • R2 R3  —  Backbone routers
    • R5 R3  —  Level 2 Only to a Level 1-2 routers
    • R4 R3  — Level 1 router to a Level 1-2 routers




    R3 Configurations:
     interface Loopback3
     ip address 30.30.30.30 255.255.255.255

    interface GigabitEthernet1/0
     ip address 172.16.23.3 255.255.255.0
     ip router isis
     negotiation auto
    !
    interface GigabitEthernet2/0
     ip address 172.16.34.3 255.255.255.0
     ip router isis
     negotiation auto
    !
    interface GigabitEthernet3/0
     ip address 172.16.35.3 255.255.255.0
     ip router isis
     negotiation auto
    !
    router isis
     net 49.0034.0000.0000.0003.00
     net 49.0035.0000.0000.0003.00

    R3#show isis neighbors

    System Id      Type Interface   IP Address      State Holdtime Circuit Id
    R2             L2   Gi1/0       172.16.23.2     UP    22       R3.03
    R4             L1   Gi2/0       172.16.34.4     UP    9        R4.01

    R5             L2   Gi3/0       172.16.35.5     UP    7        R5.01


    R3#show isis database verbose

    IS-IS Level-1 Link State Database:
    LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime      ATT/P/OL
    R3.00-00            * 0x0000000C   0x890D        851               1/0/0
      Area Address: 49.0034
      Area Address: 49.0035
      NLPID:        0xCC
      Hostname: R3
      IP Address:   172.16.35.3
      Metric: 10         IP 172.16.34.0 255.255.255.0
      Metric: 10         IP 172.16.35.0 255.255.255.0
      Metric: 10         IP 172.16.23.0 255.255.255.0
      Metric: 10         IS R4.01
    R4.00-00              0x0000000B   0xF71A        792               0/0/0
      Area Address: 49.0034
      NLPID:        0xCC
      Hostname: R4
      IP Address:   40.40.40.40
      Metric: 10         IP 40.40.40.40 255.255.255.255
      Metric: 10         IP 172.16.34.0 255.255.255.0
      Metric: 10         IS R4.01
    R4.01-00              0x00000007   0xAE98        764               0/0/0
      Metric: 0          IS R4.00
      Metric: 0          IS R3.00
    IS-IS Level-2 Link State Database:
    LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime      ATT/P/OL
    R2.00-00              0x0000000D   0x694B        692               0/0/0
      Area Address: 49.0012
      NLPID:        0xCC
      Hostname: R2
      IP Address:   20.20.20.20
      Metric: 10         IS R3.03
      Metric: 20         IP 10.10.10.10 255.255.255.255
      Metric: 10         IP 20.20.20.20 255.255.255.255
      Metric: 10         IP 172.16.12.0 255.255.255.0
      Metric: 10         IP 172.16.23.0 255.255.255.0
    R3.00-00            * 0x0000000D   0x5B62        610               0/0/0
      Area Address: 49.0034
      Area Address: 49.0035
      NLPID:        0xCC
      Hostname: R3
      IP Address:   172.16.35.3
      Metric: 10         IS R3.03
      Metric: 10         IS R5.01
      Metric: 20         IP 40.40.40.40 255.255.255.255
      Metric: 10         IP 172.16.23.0 255.255.255.0
      Metric: 10         IP 172.16.34.0 255.255.255.0
      Metric: 10         IP 172.16.35.0 255.255.255.0
    R3.03-00            * 0x00000006   0x15BA        815               0/0/0
      Metric: 0          IS R3.00
      Metric: 0          IS R2.00
    R5.00-00              0x0000000A   0x6B50        1063              0/0/0
      Area Address: 49.0035
      NLPID:        0xCC
      Hostname: R5
      IP Address:   50.50.50.50
      Metric: 10         IS R5.01
      Metric: 10         IP 50.50.50.50 255.255.255.255
      Metric: 10         IP 172.16.35.0 255.255.255.0
    R5.01-00              0x00000007   0x4685        1148              0/0/0
      Metric: 0          IS R5.00
      Metric: 0          IS R3.00

    R3#


    R3#show ip route isis
    Codes: L – local, C – connected, S – static, R – RIP, M – mobile, B – BGP
           D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
           N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
           E1 – OSPF external type 1, E2 – OSPF external type 2
           i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
           ia – IS-IS inter area, * – candidate default, U – per-user static route
           o – ODR, P – periodic downloaded static route, H – NHRP, l – LISP
           + – replicated route, % – next hop override
    Gateway of last resort is not set
          10.0.0.0/32 is subnetted, 1 subnets
    i L2     10.10.10.10 [115/30] via 172.16.23.2, 01:55:31, GigabitEthernet1/0
          20.0.0.0/32 is subnetted, 1 subnets
    i L2     20.20.20.20 [115/20] via 172.16.23.2, 01:55:31, GigabitEthernet1/0
          40.0.0.0/32 is subnetted, 1 subnets
    i L1     40.40.40.40 [115/20] via 172.16.34.4, 02:05:14, GigabitEthernet2/0
          50.0.0.0/32 is subnetted, 1 subnets
    i L2     50.50.50.50 [115/20] via 172.16.35.5, 01:57:53, GigabitEthernet3/0
          172.16.0.0/16 is variably subnetted, 7 subnets, 2 masks
    i L2     172.16.12.0/24 [115/20] via 172.16.23.2, 01:55:31, GigabitEthernet1/0
    R3#


    R3 will have the prefix with all its connected interface that are advertised into IS-IS and the prefix it learned from both the Level-1 routers and Level-2 routers.




    R4: 
    interface Loopback4

     ip address 40.40.40.40 255.255.255.255

     ip router isis

    !

    interface GigabitEthernet1/0

     no ip address

     shutdown

     negotiation auto

    !

    interface GigabitEthernet2/0

     ip address 172.16.34.4 255.255.255.0

     ip router isis

     negotiation auto

    !

    router isis

     net 49.0034.0000.0000.0004.00

     is-type level-1

    IS-IS Neighbors: 
    R4#show isis neighbors

    System Id      Type Interface   IP Address      State Holdtime Circuit Id
    R3             L1   Gi2/0       172.16.34.3     UP    23       R4.01
    R4#



    LSP Database:

    R4#show isis database verbose

    IS-IS Level-1 Link State Database:
    LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime      ATT/P/OL
    R3.00-00              0x00000010   0x8111        688               1/0/0
      Area Address: 49.0034
      Area Address: 49.0035
      NLPID:        0xCC
      Hostname: R3
      IP Address:   172.16.35.3
      Metric: 10         IP 172.16.34.0 255.255.255.0
      Metric: 10         IP 172.16.35.0 255.255.255.0
      Metric: 10         IP 172.16.23.0 255.255.255.0
      Metric: 10         IS R4.01
    R4.00-00            * 0x0000000E   0xF11D        394               0/0/0
      Area Address: 49.0034
      NLPID:        0xCC
      Hostname: R4
      IP Address:   40.40.40.40
      Metric: 10         IP 40.40.40.40 255.255.255.255
      Metric: 10         IP 172.16.34.0 255.255.255.0
      Metric: 10         IS R4.01
    R4.01-00            * 0x0000000B   0xA69C        955               0/0/0
      Metric: 0          IS R4.00
      Metric: 0          IS R3.00
    R4#

    :


    R4#show ip route isis
    Codes: L – local, C – connected, S – static, R – RIP, M – mobile, B – BGP
           D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
           N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
           E1 – OSPF external type 1, E2 – OSPF external type 2
           i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
           ia – IS-IS inter area, * – candidate default, U – per-user static route
           o – ODR, P – periodic downloaded static route, H – NHRP, l – LISP
           + – replicated route, % – next hop override

    Gateway of last resort is 172.16.34.3 to network 0.0.0.0

    i*L1  0.0.0.0/0 [115/10] via 172.16.34.3, 02:05:12, GigabitEthernet2/0
          172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
    i L1     172.16.23.0/24 [115/20] via 172.16.34.3, 02:05:21, GigabitEthernet2/0
    i L1     172.16.35.0/24 [115/20] via 172.16.34.3, 02:07:44, GigabitEthernet2/0
    R4#

     As observed R4 also have injected a default route. Since R4 is a Level-1 router, it will only learned prefixes advertise on Area 34 and a default route.


    R5:
     interface Loopback5
     ip address 50.50.50.50 255.255.255.255
     ip router isis
    interface GigabitEthernet3/0
     ip address 172.16.35.5 255.255.255.0
     ip router isis
     negotiation auto
    !
    router isis
     net 49.0035.0000.0000.0005.00
     is-type level-2-only
     R5#show isis database verbose


    IS-IS Level-2 Link State Database:
    LSPID                 LSP Seq Num  LSP Checksum  LSP Holdtime      ATT/P/OL
    R2.00-00              0x00000018   0x5356        999               0/0/0
      Area Address: 49.0012
      NLPID:        0xCC
      Hostname: R2
      IP Address:   20.20.20.20
      Metric: 10         IS R3.03
      Metric: 20         IP 10.10.10.10 255.255.255.255
      Metric: 10         IP 20.20.20.20 255.255.255.255
      Metric: 10         IP 172.16.12.0 255.255.255.0
      Metric: 10         IP 172.16.23.0 255.255.255.0
    R3.00-00              0x00000018   0x456D        720               0/0/0
      Area Address: 49.0034
      Area Address: 49.0035
      NLPID:        0xCC
      Hostname: R3
      IP Address:   172.16.35.3
      Metric: 10         IS R3.03
      Metric: 10         IS R5.01
      Metric: 20         IP 40.40.40.40 255.255.255.255
      Metric: 10         IP 172.16.23.0 255.255.255.0
      Metric: 10         IP 172.16.34.0 255.255.255.0
      Metric: 10         IP 172.16.35.0 255.255.255.0
    R3.03-00              0x00000011   0xFEC5        881               0/0/0
      Metric: 0          IS R3.00
      Metric: 0          IS R2.00
    R5.00-00            * 0x00000014   0x575A        594               0/0/0
      Area Address: 49.0035
      NLPID:        0xCC
      Hostname: R5
      IP Address:   50.50.50.50
      Metric: 10         IS R5.01
      Metric: 10         IP 50.50.50.50 255.255.255.255
      Metric: 10         IP 172.16.35.0 255.255.255.0
    R5.01-00            * 0x00000011   0x328F        515               0/0/0
      Metric: 0          IS R5.00
      Metric: 0          IS R3.00

    R5#

     Routes/Prefixes received by R5. 

    R5#show ip route isis
    Codes: L – local, C – connected, S – static, R – RIP, M – mobile, B – BGP
           D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
           N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
           E1 – OSPF external type 1, E2 – OSPF external type 2
           i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
           ia – IS-IS inter area, * – candidate default, U – per-user static route
           o – ODR, P – periodic downloaded static route, H – NHRP, l – LISP
           + – replicated route, % – next hop override

    Gateway of last resort is not set

          10.0.0.0/32 is subnetted, 1 subnets
    i L2     10.10.10.10 [115/40] via 172.16.35.3, 03:34:45, GigabitEthernet3/0
          20.0.0.0/32 is subnetted, 1 subnets
    i L2     20.20.20.20 [115/30] via 172.16.35.3, 03:34:45, GigabitEthernet3/0
          40.0.0.0/32 is subnetted, 1 subnets
    i L2     40.40.40.40 [115/30] via 172.16.35.3, 03:37:07, GigabitEthernet3/0
          172.16.0.0/16 is variably subnetted, 5 subnets, 2 masks
    i L2     172.16.12.0/24 [115/30] via 172.16.35.3, 03:34:45, GigabitEthernet3/0
    i L2     172.16.23.0/24 [115/20] via 172.16.35.3, 03:34:45, GigabitEthernet3/0
    i L2     172.16.34.0/24 [115/20] via 172.16.35.3, 03:37:07, GigabitEthernet3/0
    R5#

    Tips:
    Level-2 routers will only received Level-2 LSP’s. In case of R5, it only has the L2 prefixes from other areas.
    Let’s check the connectivity between the routers:

    From R4 towards R1 ( Level-1 router in Area 34 to another Level-1 router in Area 12):
    R4#ping 10.10.10.10 source 40.40.40.40
    Type escape sequence to abort.
    Sending 5, 100-byte ICMP Echos to 10.10.10.10, timeout is 2 seconds:
    Packet sent with a source address of 40.40.40.40
    !!!!!
    Success rate is 100 percent (5/5), round-trip min/avg/max = 24/40/60 ms
    R4#traceroute 10.10.10.10 source 40.40.40.40
    Type escape sequence to abort.
    Tracing the route to 10.10.10.10
    VRF info: (vrf in name/id, vrf out name/id)
      1 172.16.34.3 40 msec 28 msec 12 msec
      2 172.16.23.2 12 msec 32 msec 28 msec
      3 172.16.12.1 56 msec 44 msec 12 msec
    R4#
    From R1 ( Level-1 router) in Area 12 to R5 ( Level-2 router) in Area 35.
    R1#ping 50.50.50.50 source 10.10.10.10
    Type escape sequence to abort.
    Sending 5, 100-byte ICMP Echos to 50.50.50.50, timeout is 2 seconds:
    Packet sent with a source address of 10.10.10.10
    !!!!!
    Success rate is 100 percent (5/5), round-trip min/avg/max = 12/34/68 ms

    R1#traceroute 50.50.50.50 source 10.10.10.10
    Type escape sequence to abort.
    Tracing the route to 50.50.50.50
    VRF info: (vrf in name/id, vrf out name/id)
      1 172.16.12.2 4 msec 20 msec 24 msec
      2 172.16.23.3 12 msec 24 msec 32 msec
      3 172.16.35.5 76 msec 48 msec 44 msec
    R1#

    ###################################END#########################################

    Leave a comment

    Previous Post
    Next Post

    Recent posts

    Quote of the week

    "People ask me what I do in the winter when there's no baseball. I'll tell you what I do. I stare out the window and wait for spring."

    ~ Rogers Hornsby

    NETWORK LESSON

    About

    Passionate about simplifying the complex world of networking and automation for learners everywhere.”.

    Topics

    Follow Us

    Create a website or blog at WordPress.com