Interview Questions.

Question 1. What Is Acl?

Answer :

Access Control List is a packet filtering approach that filters the IP packets primarily based on source and vacation spot deal with. It is a fixed of policies and conditions that allow or deny IP packets to exercise manage over network traffic.

Question 2. What Are Different Types Of Acl?

Answer :

There are  primary varieties of Access lists:-

Standard Access List.
Extended Access List.
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Question three. Explain Standard Access List?

Answer :

Standard Access List examines only the supply IP deal with in an IP packet to permit or deny that packet. It can not in shape different area inside the IP packet. Standard Access List may be created using the get right of entry to-list numbers 1-ninety nine or inside the elevated variety of 1300-1999. Standard Access List ought to be implemented close to vacation spot. As we're filtering primarily based simplest on source address, if we positioned the usual get admission to-list near the source host or network than nothing might be forwarded from supply.

Example:-

R1 (config) # access-list 10 deny host 192.168.1.1
R1 (config) # int fa0/zero
R1 (config-if) # ip access-group 10 in
Question four. Explain Extended Access List?

Answer :

Extended Access List filters the network site visitors based totally on the Source IP deal with, Destination IP cope with, Protocol Field in the Network layer, Port quantity area on the Transport layer. Extended Access List tiers from one hundred to 199, In multiplied variety 2000-2699. Extended Access List must be located as close to source as possible. Since extended get right of entry to list filters the visitors based on particular addresses (Source IP, Destination IP) and protocols we don’t need our traffic to traverse the whole network just to be denied losing the bandwidth.

Example:-

R1 (config) # get admission to-list 110 deny tcp any host 192.168.1.1 eq 23
R1 (config) # int fa0/0
R1 (config-if) # ip get entry to-institution 110 in
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Question five. Explain Named Acl And Its Advantages Over Number Acl?

Answer :

It is just another manner of creating Standard and Extended ACL. In Named ACL names are given to become aware of access-list.

It has following gain over Number ACL - In Name ACL we are able to supply collection range which means we can insert a brand new announcement in middle of ACL.

Example:-

R1 (config) # ip get right of entry to-list extended CCNA
R1 (config) # 15 allow tcp host 10.1.1.1 host 20.1.1.1 eq 23
R1 (config) # exit
This will insert above declaration at Line 15.
R1 (config) # int fa0/0
R1 (config-if) # ip get entry to-organization ccna in
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Question 6. What Is Wildcard Mask?

Answer :

Wildcard mask is used with ACL to specify an character hosts, a community, or a variety of network. Whenever a zero is present, it indicates that octet in the address should in shape the corresponding reference precisely. Whenever a 255 is gift, it indicates those octets need no longer to be evaluated.

Wildcard Mask is absolutely contrary to subnet mask.

Example:- For /24

Subnet Mask - 255.255.255.Zero
Wildcard Mask - zero.Zero.Zero.255
Question 7. How To Permit Or Deny Specific Host In Acl?

Answer :

1. Using a wildcard mask "0.0.Zero.Zero"

Example: - 192.168.1.1 zero.Zero.0.0 or

2. Using key-word "Host"

Example: - Host 192.168.1.1

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Question eight. In Which Directions We Can Apply An Access List?

Answer :

We can apply get right of entry to listing in two guidelines:-

IN - ip get entry to-institution 10 in
OUT - ip access-institution 10 out
Question nine. Difference Between Inbound Access-listing And Outbound Access-listing?

Answer :

When an get entry to-list is carried out to inbound packets on interface, the ones packets are first processed through ACL after which routed. Any packets which can be denied received’t be routed. When an get right of entry to-listing is implemented to outbound packets on interface, those packets are first routed to outbound interface and than processed via ACL.

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Question 10. Difference Between #sh Access-list Command And #sh Run Access-list Command?

Answer :

#sh get right of entry to-listing indicates number of Hit Counts.
#sh run get entry to-listing does no longer display range of Hit Counts.
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Question 11. How Many Access Lists Can Be Applied To An Interface On A Cisco Router?

Answer :

We can assign handiest one get entry to list consistent with interface in step with protocol in keeping with path which means that that when growing an IP get admission to lists, we are able to have handiest one inbound get entry to listing and one outbound get admission to listing in step with interface. Multiple get admission to lists are accredited in keeping with interface, but they must be for a special protocol.

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Question 12. How Access Lists Are Processed?

Answer :

Access lists are processed in sequential, logical order, evaluating packets from the top down, one announcement at a time. As soon as a suit is made, the allow or deny choice is implemented, and the packet isn't always evaluated against any extra get admission to listing statements. Because of this, the order of the statements within any get right of entry to listing is full-size. There is an implicit “deny” on the stop of every access list because of this that if a packet does not healthy the condition on any of the strains inside the get right of entry to listing, the packet could be discarded.

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Question 13. What Is At The End Of Each Access List?

Answer :

At the cease of each access list, there is an implicit deny statement denying any packet for which the suit has not been found in the get admission to listing.

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Question 14. What Is The Function Of Access-list?

Answer :

Access-List goes to clear out incoming in addition to outgoing site visitors at the router interface.

Question 15. What Is The Default Wildcard Mask For Access-listing?

Answer :

Default Wild Card Mask for Access-List is zero.Zero.Zero.0

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Question 16. How Many Access-lists Can Be Created On The Router?

Answer :

1 in step with Interface
1 consistent with Direction
1 according to Protocol
Question 17. What Are The Advantages Of Standard Acl?

Answer :

Simple Packet Filtering Purpose
Limiting Access on VTY traces
Route Filtering
NAT
Route- MAPs
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Question 18. What Are The Advantages Of Extended Acl?

Answer :

Complex Packet Filtering Purpose
Route Filtering
VPN
TCP Intercept
IOS Firewall
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Question 19. What Is The Difference Between Standard Acl And Extended Acl?

Answer :

Standard ACL handiest assessments Source IP address, Extended ACL checks Source IP, Destination IP and Protocol additionally for filtering traffic.
Standard ACL can be created using range (1-ninety nine, 1300-1399) and Extended ACL may be created using number (one hundred-199, 2000-2699).
Two manner communique is blocked in Standard ACL, One way verbal exchange is stopped in Extended ACL.
Standard ACL carried out near to destination, Extended ACL implemented close to to Source.
Question 20. What Is The Difference Between Numbered Acl And Named Acl?

Answer :

Numbered ACL is created via the use of variety; Named ACL is created with the aid of the usage of name,
Removing of particular assertion isn't feasible in Numbered ACL, It is viable in Named ACL.
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Question 21. What Is The Difference Between Ipv4 Acl And Ipv6 Acl?

Answer :

No general ACL in IPV6
No wildcard mask in IPV6 ACL
In IPV6 best Named ACL's are available, there may be no numbered ACL.
Question 22. What Is The Difference Between Access-group And Access-elegance Command?

Answer :

Access-organization command is used to filter site visitors on the Interface (Ethernet, Serial).
Access-class command is used to clear out site visitors on Lines (Vty, Console, aux).
Question 23. What Is The Default Action Of Acl, If No Condition Matches In Acl?

Answer :

Drop traffic.

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Question 24. Which Traffic Is Not Filtered By Acl?

Answer :

Traffic this is generated by way of the router itself, ACL goes to clear out simplest transit site visitors.

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