ISIS ATT Bit

chargenchargen Member Posts: 12 ■□□□□□□□□□
in CCNP
Failed my first go at BSCI and am ramping up for another shot next Monday. Quick Q about ISIS and the ATT Bit.

If I perform the following steps on two routers each with an Ethernet connection to the same switch:
- enable isis (router isis)
- set the NET ( net 49.0001.0010.0100.3001.00 and a different address on the 2nd router)
- leave the first router as L1/L2 default
- change the second router to L1 using is-type level-1
- I should see the L1/L2 router having the ATT bit set to 1 via 'show isis database' and should also automatically have a default route to the L1/L2 router, correct?

What I'm seeing is no ATT bit and no default route on the 2nd router.

Thanks
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Comments

  • billscott92787billscott92787 Member Posts: 933
    chargen wrote: »
    Failed my first go at BSCI and am ramping up for another shot next Monday. Quick Q about ISIS and the ATT Bit.

    If I perform the following steps on two routers each with an Ethernet connection to the same switch:
    - enable isis (router isis)
    - set the NET ( net 49.0001.0010.0100.3001.00 and a different address on the 2nd router)
    - leave the first router as L1/L2 default
    - change the second router to L1 using is-type level-1
    - I should see the L1/L2 router having the ATT bit set to 1 via 'show isis database' and should also automatically have a default route to the L1/L2 router, correct?

    I do not believe this is correct.

    What I'm seeing is no ATT bit and no default route on the 2nd router.

    Thanks


    Are you enabling ISIS on the routers on a per-interface basis by going to the interfaces connecting and entering the command: ip router isis ? ISIS must be enabled on a per-interface basis just like IPv6 is. In addition, I believe that with IS-IS the level's a level 1 router is only going to know about routers within the intra-area. With a level 1-2 router it is an "inter-area" router. A default route isn't instantly redistributed with ISIS; you have to configure it to redistribute a default route into the IS-IS routing domain.
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  • deth1kdeth1k Member Posts: 312
    ATT is set only for inter-area routes so you wont see it with the proposed setup
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  • chargenchargen Member Posts: 12 ■□□□□□□□□□
    billscott92787 wrote: »
    Are you enabling ISIS on the routers on a per-interface basis by going to the interfaces connecting and entering the command: ip router isis ? ISIS must be enabled on a per-interface basis just like IPv6 is. In addition, I believe that with IS-IS the level's a level 1 router is only going to know about routers within the intra-area. With a level 1-2 router it is an "inter-area" router. A default route isn't instantly redistributed with ISIS; you have to configure it to redistribute a default route into the IS-IS routing domain.

    Yes, sorry - I did enter the 'ip router isis' command on the relevant interfaces on both routers. The adjacency is established and routes are being passed between the routers.

    This is what I'm thinking if:
    Getting back to routing issues, the question you asked was about a default route. So how does the 0.0.0.0/0 route show up in an IS-IS network? There are a few ways to do this.

    To begin with, you need to look at whether you're running multiple areas. If you have Level 1 routers and Level 1-2 routers, you may have it already happening. In the default implementation of IS-IS (RFC 1195), Level 1-2 routers will automatically (and ONLY) inject a default route back into the Level 1 routers they speak with.
    from: TCPmag.com | Q and A: How does IS-IS routing advertise the default route?

    Now deth1k does go a deal further toward explaining this, but I've entered the following into the config on the first and still no success in pushing out it's default route.

    2651xm config (relevant portions):
    router isis
    net 49.0001.0010.0100.1001.00
    redistribute static ip metric 5
    default-information originate
    Then, under each interface in use for ISIS:
    ip router isis

    2610 config (relevant portions):
    router isis
    net 49.0001.0010.0100.3001.00
    is-type level-1

    Even after adding the 'redistribute static' and 'default-information originate' the default route is not being sent:
    2651xm 'sh isis database detail':
    cisco2651xm#sh isis database detail

    IS-IS Level-1 Link State Database:
    LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
    cisco2651xm.00-00 * 0x00000019 0x35FA 997 0/0/0
    Area Address: 49.0001
    NLPID: 0xCC
    Hostname: cisco2651xm
    IP Address: 1.1.1.1
    Metric: 10 IP 192.168.16.0 255.255.255.252
    Metric: 10 IP 1.1.1.0 255.255.255.0
    Metric: 10 IS cisco2610.02
    cisco2610.00-00 0x000003DC 0x6AC1 917 0/0/0
    Area Address: 49.0001
    NLPID: 0xCC
    Hostname: cisco2610
    IP Address: 1.1.3.1
    Metric: 10 IP 192.168.16.0 255.255.255.252
    Metric: 10 IP 192.168.17.0 255.255.255.252
    Metric: 10 IP 192.168.18.0 255.255.255.252
    Metric: 10 IP 1.1.3.0 255.255.255.0
    Metric: 10 IS cisco2610.02
    Metric: 10 IS 0010.0100.4001.00
    cisco2610.02-00 0x00000012 0xD6C8 1091 0/0/0
    Metric: 0 IS cisco2610.00
    Metric: 0 IS cisco2651xm.00
    0010.0100.4001.00-00 0x000003DE 0xD957 976 0/0/0
    Area Address: 49.0001
    NLPID: 0xCC
    IP Address: 192.168.17.2
    Metric: 10 IP 192.168.14.0 255.255.255.0
    Metric: 10 IP 1.1.4.0 255.255.255.0
    Metric: 10 IP 192.168.17.0 255.255.255.0
    Metric: 10 IS 0010.0100.4001.02
    Metric: 10 IS cisco2610.00
    Metric: 10 IS cisco1811.01
    Metric: 0 ES 0010.0100.4001
    cisco1811.00-00 0x000003C4 0x13BF 828 0/0/0
    Area Address: 49.0001
    NLPID: 0xCC
    Hostname: cisco1811
    IP Address: 1.1.6.1
    Metric: 10 IP 192.168.14.0 255.255.255.252
    Metric: 10 IP 192.168.19.0 255.255.255.252
    Metric: 10 IP 1.1.6.1 255.255.255.255
    Metric: 10 IS cisco1811.01
    cisco1811.01-00 0x000003C3 0xB8A0 621 0/0/0
    Metric: 0 IS cisco1811.00
    Metric: 0 IS 0010.0100.4001.00
    IS-IS Level-2 Link State Database:
    LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
    cisco2651xm.00-00 * 0x00000005 0xB653 483 0/0/0
    Area Address: 49.0001
    NLPID: 0xCC
    Hostname: cisco2651xm
    IP Address: 1.1.1.1
    Metric: 0 IP 0.0.0.0 0.0.0.0
    Metric: 10 IP 1.1.1.0 255.255.255.0
    Metric: 5 IP-External 1.1.2.1 255.255.255.255
    Metric: 20 IP 1.1.3.0 255.255.255.0
    Metric: 30 IP 1.1.4.0 255.255.255.0
    Metric: 40 IP 1.1.6.1 255.255.255.255
    Metric: 40 IP 192.168.14.0 255.255.255.252
    Metric: 30 IP 192.168.14.0 255.255.255.0
    Metric: 10 IP 192.168.16.0 255.255.255.252
    Metric: 20 IP 192.168.17.0 255.255.255.252
    Metric: 30 IP 192.168.17.0 255.255.255.0
    Metric: 20 IP 192.168.18.0 255.255.255.252
    Metric: 40 IP 192.168.19.0 255.255.255.252
    cisco2651xm#
    cisco2651xm#

    2610 'sh ip route' output:
    cisco2610#sh ip route
    Codes: 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

    Gateway of last resort is not set

    1.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
    i L1 1.1.1.0/24 [115/20] via 192.168.16.2, Ethernet0/0
    C 1.1.3.0/24 is directly connected, Loopback0
    i L1 1.1.4.0/24 [115/20] via 192.168.17.2, Serial0/0
    i L1 1.1.6.1/32 [115/30] via 192.168.17.2, Serial0/0
    192.168.14.0/24 is variably subnetted, 2 subnets, 2 masks
    i L1 192.168.14.0/30 [115/30] via 192.168.17.2, Serial0/0
    i L1 192.168.14.0/24 [115/20] via 192.168.17.2, Serial0/0
    192.168.17.0/24 is variably subnetted, 2 subnets, 2 masks
    C 192.168.17.0/30 is directly connected, Serial0/0
    i L1 192.168.17.0/24 [115/20] via 192.168.17.2, Serial0/0
    192.168.16.0/30 is subnetted, 1 subnets
    C 192.168.16.0 is directly connected, Ethernet0/0
    192.168.19.0/30 is subnetted, 1 subnets
    i L1 192.168.19.0 [115/30] via 192.168.17.2, Serial0/0
    192.168.18.0/30 is subnetted, 1 subnets
    C 192.168.18.0 is directly connected, Serial0/1
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  • billscott92787billscott92787 Member Posts: 933
    :D I was pretty sure that was probably what was going on. I know when I was doing my BSCI and was learning about IS-IS, I did it a few times as well so don't feel bad there. I was so use to just using router rip, router eigrp AS, router ospf process-id. That I thought IS-IS would be the same way. It was easier to remember after getting into IPV6 since it works the same way! Glad to see things are up and running. Supposedly you can redistribute using a route-map or Cisco's website even says that you can use the default-information originate command. icon_thumright.gif

    What was your score on your 1st shot at the BSCI? What are you using to prepare? Also, what areas do you feel that you scored the worst in? I failed my first BSCI shot as well, so don't feel bad there. I needed a 790 to pass I believe and got a 783.
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  • chargenchargen Member Posts: 12 ■□□□□□□□□□
    billscott92787 wrote: »
    :D I was pretty sure that was probably what was going on. I know when I was doing my BSCI and was learning about IS-IS, I did it a few times as well so don't feel bad there. I was so use to just using router rip, router eigrp AS, router ospf process-id. That I thought IS-IS would be the same way. It was easier to remember after getting into IPV6 since it works the same way! Glad to see things are up and running. Supposedly you can redistribute using a route-map or Cisco's website even says that you can use the default-information originate command. icon_thumright.gif

    While I got BSCI up and running, still no default route being created. When I entered the default-information originate in OSPF on the 2651xm the 'gateway of last resort' got set no problem :-/
    What was your score on your 1st shot at the BSCI? What are you using to prepare? Also, what areas do you feel that you scored the worst in? I failed my first BSCI shot as well, so don't feel bad there. I needed a 790 to pass I believe and got a 783.

    I used the Cisco press official book and got a 591 I think it was. Woefully unprepared for some of the redistribution and troubleshooting questions. Got stuck on an EIGRP question for far too long and wound up running out of time.

    Practice makes perfect - or at least a 790 icon_smile.gif

    Thanks

    -Pete
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  • deth1kdeth1k Member Posts: 312
    Hi chargen,

    Looking at the configs both of your routers are still in the same area therefore no default route is being injected into L1. You need a 3rd router in this lab in another area if you want to see this working.

    something like:

    R1 (49.0001.1111.1111.1111.00)
    R2(49.0002.2222.2222.2222.00)
    R3(49.0002.3333.3333.333.00)

    R2 being L1/2 and R3 being L1

    Cheers
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  • billscott92787billscott92787 Member Posts: 933
    deth1k wrote: »
    Hi chargen,

    Looking at the configs both of your routers are still in the same area therefore no default route is being injected into L1. You need a 3rd router in this lab in another area if you want to see this working.

    something like:

    R1 (49.0001.1111.1111.1111.00)
    R2(49.0002.2222.2222.2222.00)
    R3(49.0002.3333.3333.333.00)

    R2 being L1/2 and R3 being L1

    Cheers

    You actually don't need three routers to see the default route distributed; but you can if you prefer it. I agree that these need to be defined as different areas though.

    The fact of the matter is that your routers would either have to be a L1-L2 router. The L1 router would only accept advertisements from an intra-area router. As you can see if I have R2 defined as L1, no default route is accepted by R2.

    See below:


    R2 routing table (after enabling L1 type on R2)
    C 192.168.1.0/24 is directly connected, Serial0/0
    R2#



    After defining R2 as an L1-L2 router, you can see the default route.

    R2 routing table (as an L1-L2 router):
    C 192.168.1.0/24 is directly connected, Serial0/0
    i*L2 0.0.0.0/0 [115/10] via 192.168.1.1, Serial0/0
    R2#
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  • deth1kdeth1k Member Posts: 312
    Hi billscott92787,

    Isn't it what i've said?

    "R2 being L1/2"
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  • billscott92787billscott92787 Member Posts: 933
    Yeah but you indicated him having to add a 3rd router, which isn't the case icon_thumright.gif
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  • chargenchargen Member Posts: 12 ■□□□□□□□□□
    billscott92787 wrote: »
    Yeah but you indicated him having to add a 3rd router, which isn't the case icon_thumright.gif

    I do have a third router and I think it's even capable of running ISIS! icon_smile.gif

    I did a bit of testing in that I changed the 2651xm to be in a different area but didn't have much success.
    I think I can sneak in one last test, so I'll do the following to have a router set the ATT bit, correct?

    R1: L1 - Area 1
    R2: L1/L2 - Area 2
    R3: L1/L2 - Area 3

    And on R1 I should see R2 sending it's hellos with the ATT bit set?
    -Pete
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  • deth1kdeth1k Member Posts: 312
    Make R1 and R2 part of the same area ;)
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  • chargenchargen Member Posts: 12 ■□□□□□□□□□
    deth1k wrote: »
    Make R1 and R2 part of the same area ;)

    Or they can't form an adjacency, right?
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  • chargenchargen Member Posts: 12 ■□□□□□□□□□
    Passed the BSCI this morning! Yay!
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  • mikej412mikej412 Member Posts: 10,086 ■■■■■■■■■■
    chargen wrote: »
    Passed the BSCI this morning!
    Congratulations!! icon_cheers.gif
    :mike: Cisco Certifications -- Collect the Entire Set!
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