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CCENT/CCNA [H] study group

Question in the book completely screwed me up, i wanna make sure i have this right

Topic: EIGRP routing protocol
==========================================================
term --- my description (hopefully im correct!)
--------------------------------------------------------------------------------------------------------------------
FD (feasable distance) --- the shortest metric distance between the current router and the destination subnet

RD (reported distance) --- the shortest metric distance between a router neighboring our current router and the destination subnet (basically a neighboring router's FD)

Sucessor --- the route with the shortest metric distance (the metric distance will be the FD)

Feasable Sucessor --- the route with the next shortest metric distance who's RD does not exceed the FD.
==========================================================

Do i have those definitions down correctly?
 
Co-worker passed CCIE R&S written this morning. Gives me some hope. 100 questions multiple choice/drag and drop.

I have mine scheduled for December, but may bump it up if I get the reading done.
 
Booked my ICND2 for the 5th of October (my birthday). Bunch of WIC-2Ts coming this week along with some serial cables and a 2801.
 
temporary.jpg


i drew that up because i wanna make sure i have that right, does all of that look correct?

I got confused when the IOS commands called one port the outside and the other the inside, yet global inside seems to refer to the source address on the outside network.
 
serpretetsky said:
temporary.jpg


i drew that up because i wanna make sure i have that right, does all of that look correct?

I got confused when the IOS commands called one port the outside and the other the inside, yet global inside seems to refer to the source address on the outside network.
Click to expand...

I saw that a lot on the PIX firewalls I have been working with. I just always remembered Inside = My stuff, may or may not be right though. With what I was doing it was though.
 
/usr/home said:
It seems to be that you need to use the map command when doing multi-point, but you can use interface-dlci when doing point-to-point. Correct?

How often do you guys actually run into these circuits? Are they still fairly common or are they more the "IRQ" section of the A+ exam? (You learn them in case you run across it, but nothing new really uses them. (Yes I know IRQs are still used but you rarely need to dick with them anymore))
Click to expand...
I'm still learning this stuff along with you, so bear with me :D.

My info is coming from Wendel Odom's, CCNA ICND2.

frame-relay map command most of the time doesn't need to be use, and isn't used at all for point to point (since there's only a single DLCI number, the router will just spit everyone destined to that ip subnet out on that single DLCI). The book even admits that in most production environments you wouldn't use the frame-relay map command, that you only need it for the exam. Most of the examples in the book use frame-relay interface-dlci command for both multipoint and point to point instead of mapping directly.

Keep in mind that activating the frame-relay map command deactives inverse arping (i think on just the DLCI, but please confirm me). Which means the other device on that DLCI will probably need to use the frame-relay map command to.

Also, i can't remember how to reactive inverse arping. Do you just use the "no frame-relay map" command?
 
Vashypooh said:
I saw that a lot on the PIX firewalls I have been working with. I just always remembered Inside = My stuff, may or may not be right though. With what I was doing it was though.
Click to expand...
yeah, i guess that usually makes sense. I guess i'm just getting confused because one concept refers to the actual networks (inside or outside network)
and the other refers to the addresses (global/local inside/outside address)
and that they're not really directly comparable.
 
serpretetsky said:
thank you, i have one more question. In packet tracer simulation software the serial cables are labeled either DTE or DCE (not the ends! the cable itself!) is this an oversimplification or perhaps just plain incorrect?
Click to expand...
oh, btw, i posted this a while ago and never really got a satisfying answer.

In packet tracer whether you choose the DTE or DCE cable they are EXACTLY THE SAME. The only difference being that if you choose the DTE cable, the FIRST port you attach to is the DTE, whereas with the DCE cable, the first port you attach to becomes the DCE.

was very confused at first.
 
jesus

i applied for a network engineer job, did a phone interview

friday had a in person interview

got emailed today to call and schedule ANOTHER interview ASAP

guess I didnt nail it
 
/usr/home said:
Booked my ICND2 for the 5th of October (my birthday). Bunch of WIC-2Ts coming this week along with some serial cables and a 2801.
Click to expand...

I just got my last few wics in and cables for my lab. Need to step up and finish my ccna asap
 
ipv6 autoconfiguration question:

When ipv6 is setup for stateless autoconfiguration on a host it gets its ip address information via NDP protocol from all routers on that segment. It also sounds like it gets its default router via this same method.

If there are multiple routers on the same segment, how does the host know which is the default router. Do the routers advertise that they have a default gateway? What if there's multiple routers with default gateways in a segment. What if I don't have any routers with default gateways but they have individual routes to all of the internet anyways and i want to use it as a default gateway?
 
Ok, so spanning-tree. Does spanning-tree care about VLANs? IE: Do you need a default VLAN for the spanning-tree hellos to go between switches? Or since it's multicast, will they still go through?

I guess my question is, does it need to be configured differently whether it's a regular port or part of an etherchannel or a trunk port? Say you have 4 switches in a ring. Can you have certain VLANs go "one-way" and other VLANs "the other way"? Or is it a all traffic either goes this or that way, not split?

Dur. Ignore my question. I rewatched the section of CBT Nuggets on STP. Makes sense now.
 
Last edited:
/usr/home said:
Ok, so spanning-tree. Does spanning-tree care about VLANs? IE: Do you need a default VLAN for the spanning-tree hellos to go between switches? Or since it's multicast, will they still go through?

I guess my question is, does it need to be configured differently whether it's a regular port or part of an etherchannel or a trunk port? Say you have 4 switches in a ring. Can you have certain VLANs go "one-way" and other VLANs "the other way"? Or is it a all traffic either goes this or that way, not split?

Dur. Ignore my question. I rewatched the section of CBT Nuggets on STP. Makes sense now.
Click to expand...

This should answer your question

http://www.cisco.com/en/US/tech/tk389/tk621/tk846/tsd_technology_support_sub-protocol_home.html
 
Starting CCNA Dis Sem 1 in September then following on with 2, 3 and 4 next year. Also starting Computer Sc degree p/t in January. Think I need my head seeing to :eek: :p Catch you on here next month probably :D
 
Vashypooh said:
I saw that a lot on the PIX firewalls I have been working with. I just always remembered Inside = My stuff, may or may not be right though. With what I was doing it was though.
Click to expand...

Code: 
My Router#show ip nat trans
Pro Inside global      Inside local       Outside local      Outside global
udp x.x.61.0:52      10.0.0.2:123       96.47.67.105:123   96.47.67.105:123
udp x.x.61.0:123     10.0.0.4:123       64.90.182.55:123   64.90.182.55:123
udp x.x.61.0:123     10.0.0.4:123       96.47.67.105:123   96.47.67.105:123
udp x.x.61.0:46      10.0.0.5:123       64.90.182.55:123   64.90.182.55:123

Here is an excerpt from my home router showing some NAT translations if this helps. I masked my inside global and hostname for privacy/security. This is just a few of my other routers and switches talking to some NTP servers.
 
/usr/home said:
Ok, so spanning-tree. Does spanning-tree care about VLANs? IE: Do you need a default VLAN for the spanning-tree hellos to go between switches? Or since it's multicast, will they still go through?

I guess my question is, does it need to be configured differently whether it's a regular port or part of an etherchannel or a trunk port? Say you have 4 switches in a ring. Can you have certain VLANs go "one-way" and other VLANs "the other way"? Or is it a all traffic either goes this or that way, not split?

Dur. Ignore my question. I rewatched the section of CBT Nuggets on STP. Makes sense now.
Click to expand...

To keep things simple the earliest implementations of spanning tree had all VLAN's share an STP instance and this was called Common Spanning Tree or CST.

Modern Cisco switches now use PVST+ by default, PVST+ creates a single instance per vlan so you can do fun stuff like load balancing by making certain switches root bridge for certain vlans

The spanning tree is created by all switches identifying the lowest cost path to the root bridge based on

1. Root Bridge ID
2, Root Path Cost
3, Sender Bridge ID
4. Sender Port Cost

All redundant, higher cost links will be blocked and not forward traffic. There are a bunch of cool features to really fine tune spanning tree that you'll learn about in SWITCH.

Wiki has a GREAT example of STP
http://en.wikipedia.org/wiki/Spanning_Tree_Protocol
 
serpretetsky said:
excuse me for summarizing my post, but i reloaded packet tracer and now my network is working perfectly :confused:. I am blaming this on packet tracer software.
Click to expand...

I would reccommend GNS3, it cant really do any switching but it is awesome for Routing since you are working with real IOS.
 
l3thal6 said:
I would reccommend GNS3, it cant really do any switching but it is awesome for Routing since you are working with real IOS.
Click to expand...
yeah, i cross check with GNS3 but didn't use it very often because mine crashed every 5 or so minutes (the dynamips system would crash, GNS3 would still be fine)

I actually just learned a lot of people are having trouble with the 2600 series router firmware in GNS3, so i just switched it to 3600 and it seems to be better, although i recently managed to crash the entire program anyways....

...in short, i'm not finding my current GNS3 solution to be the most stable, definilty having better luck with packet tracer, but i still cross check weird glitches in packet tracer with gns3.
 
I've been using the 3725 Emulator with c3725-adventerprisek9-mz.124-15.T10 for all of my ROUTE lab work thus far, put in about 8 lab hours over the last 3 days with no issues.
 
OSPF - OK, say I'm advertising 192.168.0.0 /20 and I add .17.x, .18.x, .19.x, and .20.x. Can I then advertise 192.168.0.0 /20 and 192.168.16.0 /22 ? Basically, can I do VLSM in the summarizations or do I need to use 192.168.0.0 /19 and then waste 12 networks?
 
/usr/home said:
OSPF - OK, say I'm advertising 192.168.0.0 /20 and I add .17.x, .18.x, .19.x, and .20.x. Can I then advertise 192.168.0.0 /20 and 192.168.16.0 /22 ? Basically, can I do VLSM in the summarizations or do I need to use 192.168.0.0 /19 and then waste 12 networks?
Click to expand...

Yes VLSM is supported in everything except RIPv1.
 
Frick Rack Ears are expensive. I can find them for like 5-10 bucks on eBay but the shipping is like $25 to
Canada. They charge 3 bucks to ship within the States. What a ripoff. It costs like 4 bucks to ship a set of rack ears through USPS.

Anyone know of a cheap place to get them in Canada or does anyone have any they want to get rid of? I'm looking for some for a 2801 and a 2611.
 
devin_m said:
Yes VLSM is supported in everything except RIPv1.
Click to expand...

Neither does IGRP. But yeah, pretty much any classless routing protocol.

You can also enable or disable auto-summary or make your own summary routes if you wanted to simplify the routing table. Some protocols like OSPF have it on by default.
 
Retarded. PacketTracer doesn't support the range command under OSPF. Lame. I guess it's not part of CCNA, but still....

Leader#show ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
i - IS-IS, 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

10.0.0.0/8 is variably subnetted, 5 subnets, 2 masks
O IA 10.0.0.0/30 [110/256] via 10.0.0.17, 00:00:11, Serial0/0/0
O IA 10.0.0.4/30 [110/192] via 10.0.0.17, 00:00:11, Serial0/0/0
O 10.0.0.12/30 [110/128] via 10.0.0.17, 00:00:11, Serial0/0/0
C 10.0.0.16/30 is directly connected, Serial0/0/0
O IA 10.0.1.0/24 [110/193] via 10.0.0.17, 00:00:11, Serial0/0/0
Click to expand...

So this is my routing table from one of my routers. It is in Area 1 currently. Everything is working, but I just want to verify my OSPF config. Since I can't do a range command, this looks correct? Theoretically if I could do a range command on the 10.0.0.17 router, the table should only have one line for 10.0.0.0/29, correct? Like this: O IA 10.0.0.0/29 [110/256] via 10.0.0.17, 00:00:11, Serial0/0/0
 
/usr/home said:
Frick Rack Ears are expensive. I can find them for like 5-10 bucks on eBay but the shipping is like $25 to
Canada. They charge 3 bucks to ship within the States. What a ripoff. It costs like 4 bucks to ship a set of rack ears through USPS.

Anyone know of a cheap place to get them in Canada or does anyone have any they want to get rid of? I'm looking for some for a 2801 and a 2611.
Click to expand...

nah but if its overall cheaper I would be willing to reship them for you
 
/usr/home said:
Retarded. PacketTracer doesn't support the range command under OSPF. Lame. I guess it's not part of CCNA, but still....

So this is my routing table from one of my routers. It is in Area 1 currently. Everything is working, but I just want to verify my OSPF config. Since I can't do a range command, this looks correct? Theoretically if I could do a range command on the 10.0.0.17 router, the table should only have one line for 10.0.0.0/29, correct? Like this: O IA 10.0.0.0/29 [110/256] via 10.0.0.17, 00:00:11, Serial0/0/0
Click to expand...

I don't have a scaled out OSPF lab right now, but I have a massive EIGRP one setup and I will show you the beauty of sumarization.

312014_10150985663993155_395103120_n.jpg


I removed a few routes from the routing table for this example.You can see on this side that the 10.0.64.0/18 network hasn't been summarized and the routing table is crowded and massive

Code: 
EECLTCI1#show ip route eigrp
     10.0.0.0/8 is variably subnetted, 29 subnets, 4 masks
D       10.0.74.0/24 [90/409600] via 10.0.64.1, 00:34:16, FastEthernet0/1
D       10.0.75.0/24 [90/409600] via 10.0.64.1, 00:34:16, FastEthernet0/1
D       10.0.72.0/24 [90/409600] via 10.0.64.6, 00:33:18, FastEthernet0/0
D       10.0.64.8/30 [90/307200] via 10.0.64.6, 00:42:44, FastEthernet0/0
D       10.0.73.0/24 [90/409600] via 10.0.64.1, 00:34:16, FastEthernet0/1
D       10.0.78.0/24 [90/409600] via 10.0.64.1, 00:34:16, FastEthernet0/1
D       10.0.79.0/24 [90/409600] via 10.0.64.1, 00:34:16, FastEthernet0/1
D       10.0.76.0/24 [90/409600] via 10.0.64.1, 00:34:16, FastEthernet0/1
D       10.0.64.12/30 [90/307200] via 10.0.64.1, 00:42:44, FastEthernet0/1
D       10.0.77.0/24 [90/409600] via 10.0.64.1, 00:34:16, FastEthernet0/1
D       10.0.66.0/24 [90/409600] via 10.0.64.6, 00:33:18, FastEthernet0/0
D       10.0.67.0/24 [90/409600] via 10.0.64.6, 00:33:19, FastEthernet0/0
D       10.0.64.0/18 is a summary, 00:43:21, Null0
D       10.0.65.0/24 [90/409600] via 10.0.64.6, 00:33:19, FastEthernet0/0
D       10.0.70.0/24 [90/409600] via 10.0.64.6, 00:33:19, FastEthernet0/0
D       10.0.71.0/24 [90/409600] via 10.0.64.6, 00:33:19, FastEthernet0/0
D       10.0.68.0/24 [90/409600] via 10.0.64.6, 00:33:19, FastEthernet0/0
D       10.0.69.0/24 [90/409600] via 10.0.64.6, 00:33:19, FastEthernet0/0
D       10.0.80.0/24 [90/409600] via 10.0.64.1, 00:34:17, FastEthernet0/1
D       10.0.64.16/30 [90/284160] via 10.0.64.6, 00:42:45, FastEthernet0/0
                      [90/284160] via 10.0.64.1, 00:42:45, FastEthernet0/1
D*EX 0.0.0.0/0 [170/309760] via 10.0.64.6, 00:42:48, FastEthernet0/0
               [170/309760] via 10.0.64.1, 00:42:48, FastEthernet0/1

However, when you configure this on the S0/0 interface...

Code: 
EECLTCI1#show run int s0/0
Building configuration...

Current configuration : 210 bytes
!
interface Serial0/0
 bandwidth 8000
 ip address 10.0.255.2 255.255.255.0
 encapsulation frame-relay
 ip authentication key-chain eigrp 100 EIGRP-SEC
 ip summary-address eigrp 100 10.0.64.0 255.255.192.0 5
 clock rate 8000000
 frame-relay lmi-type ansi
end

. On this side there is a single entry :D

Code: 
EELAXCI1#show ip route eigrp
     10.0.0.0/8 is variably subnetted, 13 subnets, 4 masks
D       10.0.64.0/18 [90/857600] via 10.0.255.2, 00:00:40, Serial0/0

This was done on GNS3 0.8.3
 
Last edited:
l3thal6 said:
I don't have a scaled out OSPF lab right now, but I have a massive EIGRP one setup and I will show you the beauty of sumarization.

312014_10150985663993155_395103120_n.jpg


I removed a few routes from the routing table for this example.You can see on this side that the 10.0.64.0/18 network hasn't been summarized and the routing table is crowded and massive

Code: 
EECLTCI1#show ip route eigrp
     10.0.0.0/8 is variably subnetted, 29 subnets, 4 masks
D       10.0.74.0/24 [90/409600] via 10.0.64.1, 00:34:16, FastEthernet0/1
D       10.0.75.0/24 [90/409600] via 10.0.64.1, 00:34:16, FastEthernet0/1
D       10.0.72.0/24 [90/409600] via 10.0.64.6, 00:33:18, FastEthernet0/0
D       10.0.64.8/30 [90/307200] via 10.0.64.6, 00:42:44, FastEthernet0/0
D       10.0.73.0/24 [90/409600] via 10.0.64.1, 00:34:16, FastEthernet0/1
D       10.0.78.0/24 [90/409600] via 10.0.64.1, 00:34:16, FastEthernet0/1
D       10.0.79.0/24 [90/409600] via 10.0.64.1, 00:34:16, FastEthernet0/1
D       10.0.76.0/24 [90/409600] via 10.0.64.1, 00:34:16, FastEthernet0/1
D       10.0.64.12/30 [90/307200] via 10.0.64.1, 00:42:44, FastEthernet0/1
D       10.0.77.0/24 [90/409600] via 10.0.64.1, 00:34:16, FastEthernet0/1
D       10.0.66.0/24 [90/409600] via 10.0.64.6, 00:33:18, FastEthernet0/0
D       10.0.67.0/24 [90/409600] via 10.0.64.6, 00:33:19, FastEthernet0/0
D       10.0.64.0/18 is a summary, 00:43:21, Null0
D       10.0.65.0/24 [90/409600] via 10.0.64.6, 00:33:19, FastEthernet0/0
D       10.0.70.0/24 [90/409600] via 10.0.64.6, 00:33:19, FastEthernet0/0
D       10.0.71.0/24 [90/409600] via 10.0.64.6, 00:33:19, FastEthernet0/0
D       10.0.68.0/24 [90/409600] via 10.0.64.6, 00:33:19, FastEthernet0/0
D       10.0.69.0/24 [90/409600] via 10.0.64.6, 00:33:19, FastEthernet0/0
D       10.0.80.0/24 [90/409600] via 10.0.64.1, 00:34:17, FastEthernet0/1
D       10.0.64.16/30 [90/284160] via 10.0.64.6, 00:42:45, FastEthernet0/0
                      [90/284160] via 10.0.64.1, 00:42:45, FastEthernet0/1
D*EX 0.0.0.0/0 [170/309760] via 10.0.64.6, 00:42:48, FastEthernet0/0
               [170/309760] via 10.0.64.1, 00:42:48, FastEthernet0/1

However, when you configure this on the S0/0 interface...

Code: 
EECLTCI1#show run int s0/0
Building configuration...

Current configuration : 210 bytes
!
interface Serial0/0
 bandwidth 8000
 ip address 10.0.255.2 255.255.255.0
 encapsulation frame-relay
 ip authentication key-chain eigrp 100 EIGRP-SEC
 ip summary-address eigrp 100 10.0.64.0 255.255.192.0 5
 clock rate 8000000
 frame-relay lmi-type ansi
end

. On this side there is a single entry :D

Code: 
EELAXCI1#show ip route eigrp
     10.0.0.0/8 is variably subnetted, 13 subnets, 4 masks
D       10.0.64.0/18 [90/857600] via 10.0.255.2, 00:00:40, Serial0/0

This was done on GNS3 0.8.3
Click to expand...

So how exactly do you setup GNS3? Can you put it on a regular desktop or do you need a computer with a bunch of NICs? Is it like PacketTracer in that you can run it within Windows?

Ok I have it installed here. Can you add other routers like a 2801 or are you stuck with the ones in there?
 
Last edited:
GNS3 doesn't really need anything special, but I would recommend 4GB of RAM and at least a 2 core CPU.

You just install it within Windows, Mac OSX or Linux, there are a few things you need to configure but within 5 minutes you can be building networks.

You will need the following:

gns3 all in one http://www.gns3.net/download/

gns3 documentation http://www.gns3.net/gns3-quick-start-windows/

A Cisco IOS (I am using c3725-adventerprisek9-mz.124-15.T10) ...I heard you may be able to find these pretty easily ;)

The most important thing for performance is to set the IDLE PC value!
 
GNS3 is limited to what hardware is installed :(

It is based on dynamips which hasn't been updated for a few years :(

Once I start my CCIE studies I will probably have to build a mostly hardware lab.
 
Last edited:
one of the labs i was doing asked to create a macro. My book doesn't mention macros. Packet Tracer doesn't seem to support macros. My 3600 series router in GNS3 doesn't support the macro command. My older 2900 series xl and 3500 series xl physical switches don't support macros.

Is this a new command on newer switches and has anyone seen this tested on the CCNA?
 
serpretetsky said:
one of the labs i was doing asked to create a macro. My book doesn't mention macros. Packet Tracer doesn't seem to support macros. My 3600 series router in GNS3 doesn't support the macro command. My older 2900 series xl and 3500 series xl physical switches don't support macros.

Is this a new command on newer switches and has anyone seen this tested on the CCNA?
Click to expand...

It was skimmed over when I was studying SWITCH. One pre-configured macro is "switchport host".

Code: 
EEUSDS013550#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
EEUSDS013550(config)#int f0/1
EEUSDS013550(config-if)#switchport host
switchport mode will be set to access
spanning-tree portfast will be enabled
channel group will be disabled

EEUSDS013550(config-if)#do show run int f0/1
Building configuration...

Current configuration : 81 bytes
!
interface FastEthernet0/1
 switchport mode access
 spanning-tree portfast
end

EEUSDS013550(config-if)#end
EEUSDS013550#show ver
Cisco IOS Software, C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(52)SE, RELEASE SOFTWARE (fc3)
Copyright (c) 1986-2009 by Cisco Systems, Inc.
 
l3thal6 said:
It was skimmed over when I was studying SWITCH. One pre-configured macro is "switchport host".

Code: 
EEUSDS013550#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
EEUSDS013550(config)#int f0/1
EEUSDS013550(config-if)#switchport host
switchport mode will be set to access
spanning-tree portfast will be enabled
channel group will be disabled

EEUSDS013550(config-if)#do show run int f0/1
Building configuration...

Current configuration : 81 bytes
!
interface FastEthernet0/1
 switchport mode access
 spanning-tree portfast
end

EEUSDS013550(config-if)#end
EEUSDS013550#show ver
Cisco IOS Software, C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(52)SE, RELEASE SOFTWARE (fc3)
Copyright (c) 1986-2009 by Cisco Systems, Inc.
Click to expand...

Nice. So it does that all for you. That's handy to remember.
 
So, I am about to configure some more networks into the massive topology I have now, I am going to scale out the service provider network and put POPs in each major "city" I'll also be deploying 7200 routers in the SP cloud so I am moving the whole lab to a VM with 16GB RAM and 4 cores.
 
switchport security

ok, is this correct?
1) switchport port-security mac-address [mac address here] : will only allow the specified addresses to send frames on this port, this setting ignores maximum addresses

2) switchport port-security : will allow the switch to learn the first mac address of sending frames on this port, up to the maximum specified. These addresses are not written into any config, and are wiped after restart (but are permanent as long as the switch doesn't reboot?)

3) switchport port-security mac-address sticky : : will allow the switch to learn the first mac address of sending frames on this port, up to the maximum specified. These addresses are written to the running-config, if you issue "copy running startup" then you can allow the switch to start with these addresses preconfigured automatically. However, any mac addresses learned AFTER you issue a "copy running startup" will be lost after reboot.
 
Serial Broadcasts

temporary_framerelay.png


Here's the setup, i was asked to create this setup and setup OSPF on it.
I was also asked to statically map the ip addresses to the DLCI interfaces.

here's what i did
Code: 
 R1
frame map ip 10.0.0.2 102
frame map ip 10.0.0.3 103
Code: 
R2
frame map ip 10.0.0.1 201
frame map ip 10.0.0.3 201
Code: 
R3
frame map ip 10.0.0.1 301
frame map ip 10.0.0.2 301
You can see i didn't use the "broadcast" keyword at the end of all of those commands.

Naturally OSPF failed miserably and pings to 255.255.255.255 gave me nothing.

So next i redid all of the commands with the broadcast keyword.

Here is where i am confused. OSPF is working, but it's clearly not a true broadcast network as R2 and R3 can't see each other directly, but only through R1. A ping of 255.255.255.255 from either R2 or R3 showed replies only from R1, and 255.255.255.255 ping from R1 showed replies from both R2 and R3. Pinging the routers directly works fine though, no issues there.

Interestingly, pinging R3 from R2 shows 2 duplicate packets leaving R2 destined for 255.255.255.255 (since it has two broadcast maps) for each of the 4 attempts. But R1 accepts both of them for itself since it matches 255.255.255.255 and replies to both of them.

At this point I'm wondering what's the point of adding "broadcast" at the end of the network if its still clearly not a broadcast network. Is it simply because the ip stack defaults to not accepting 255.255.255.255 pings to a serial device and putting "broadcast" tells the ip stack to accept this ip address?

I've also noticed that the destination router doesn't forward the broadcast packet onwards to other devices on the same subnet. i guess it makes sense, i meant, it accepts the broadcast packet as destined to its own interface, why would it make a copy and forward it out on the same interface it recieved it on? Plus routers don't forward any type of broadcasts in general right?
 
serpretetsky said:
Serial Broadcasts

temporary_framerelay.png


Here's the setup, i was asked to create this setup and setup OSPF on it.
I was also asked to statically map the ip addresses to the DLCI interfaces.

here's what i did
Code: 
 R1
frame map ip 10.0.0.2 102
frame map ip 10.0.0.3 103
Code: 
R2
frame map ip 10.0.0.1 201
frame map ip 10.0.0.3 201
Code: 
R3
frame map ip 10.0.0.1 301
frame map ip 10.0.0.2 301
You can see i didn't use the "broadcast" keyword at the end of all of those commands.

Naturally OSPF failed miserably and pings to 255.255.255.255 gave me nothing.

So next i redid all of the commands with the broadcast keyword.

Here is where i am confused. OSPF is working, but it's clearly not a true broadcast network as R2 and R3 can't see each other directly, but only through R1. A ping of 255.255.255.255 from either R2 or R3 showed replies only from R1, and 255.255.255.255 ping from R1 showed replies from both R2 and R3. Pinging the routers directly works fine though, no issues there.

Interestingly, pinging R3 from R2 shows 2 duplicate packets leaving R2 destined for 255.255.255.255 (since it has two broadcast maps) for each of the 4 attempts. But R1 accepts both of them for itself since it matches 255.255.255.255 and replies to both of them.

At this point I'm wondering what's the point of adding "broadcast" at the end of the network if its still clearly not a broadcast network. Is it simply because the ip stack defaults to not accepting 255.255.255.255 pings to a serial device and putting "broadcast" tells the ip stack to accept this ip address?

I've also noticed that the destination router doesn't forward the broadcast packet onwards to other devices on the same subnet. i guess it makes sense, i meant, it accepts the broadcast packet as destined to its own interface, why would it make a copy and forward it out on the same interface it recieved it on? Plus routers don't forward any type of broadcasts in general right?
Click to expand...

You need this command on the serial interfaces as well, do you not?

Router(config-if)#ip ospf network broadcast

Also, in the real world you would just use arp instead of a map, would you not? I don't see the benefit of static maps. Security?
 
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