Encor Flashcards
Cati bytes are headerul GRE?
4 bytes
Cand folosesti GRE, cati bytes se adauga packet-ului in total?
24 bytes. 4 Gre Header, 20 New IP Header
La cat ar trebui sa setezi MTU daca folosesti GRE?
1476 bytes
Ce este Tcp Mss?
Tcp maximum size. Reprezinta cantitatea maxima de date pe care un host o poate primi intr-un singur tcp segment
Unde pot specifica hosturile MSS-ul ?
In Syn si Syn Ack
Daca nu isi specifica MSS-ul un host, care sunt valorile default?
Ipv4: 536 bytes
Ipv6: 1220 bytes
Cisco Ios devices specify an Mss of x bytes for devices in the same network and y bytes for devices in another network. What are the values of x and y?
X= 1460
Y= 536
In centralized CEF the CEF forwarding decisions are perforned on the…?
RP/RSP card
RP= Route processor card
RSP= Route switch processor card
Software based routers au control plane si data plane shared?
Da
Hardware based routers au control plane si data plane shared?
Nu. Separate
Who handles the Control Plane on Hardware Based Routers?
The CPU
Hardware based routers forwards packets using …?
ASIC.
Software Based routers control plane is in the Cpu?
Yes. Data plane also
In hybrid routers who handles the control plane? What about the Data plane?
The CPU.
The NP - Network Processor
What are the two components of CEF?
The FIB - Forwarding Information Base
The Adjency table
The fib takes its information using the..?
RIB - routing information base
The adjaceny table takes its information using the…
ARP Table
In software CEF where are stored the fib and adj table? Who processes the software CEF?
In the RAM
The CPU
In Hardware CEF where are stored the FIB and the Adj Table?
Who proccesses Hardware CEF?
The FIB is stored in TCAM and the Adj Table in a separate standalone memory.
The ASIC
Cate switchuri permite in stack Virtual Switching System (VSS)?
2
In Distributed CEF (dCEF), the CEF forwarding decisions are performed on each …?
Line Card. The Line cards each store a copy of the FIB and Adj table
What kind of traffic passes through the VSL?
VSS Control Traffic: Traffic used to establish and maintain the VSS
Data Traffic: when traffic received on one member must be sent out of an interface on the other member
In cazul VSS ( Virtual Switching System) ce anume se formeaza intre SW-uri pentru a crea stack-ul?
VSL - Virtual Switch Link
Care sunt protocoalele componente lui VLSP?
LMP si RRP
LMP Link Management Protocol
RRP Role Resolution Protocol
Ce functii performeaza LMP?
Verifies link integrity by establishing bidir traffic
Exchanges switch IDs
Exchanges other required information
Ce functii performeaza RRP?
Determina daca versiunile software si hardware ale switchurilor sunt
compatibile
Determina active si standby switch
In cate moduri se poate ridica stackul in Vss?
- RPR - Route Processor Redundancy - switchul standby nu poate forwarda trafic
(control plane, mng plane, data plane sunt in standby) - Nsf/Sso - switchul standby forwardeaza trafic
(Control plane, mng plane standby, data plane fwd)
In StackWise ce protocol se foloseste pentru a descoperi topologia stack?
SDP - Stack Discovery Protocol - broadcasteaza mesajele prin stack connections
Cate switchuri suporta stackwise virtual?
2
VSLP has two component protocols
LMP - Link Management Protocol
RRP - Role Resolution Protocol
What are the functions of LMP?
Verifies the link integrity by establishing bidrectional traffic forwarding
Exchanges switch Ids - they should be different
Exchanges other required information
What are the functions of RRP?
Determines if the hardware and software versions of the switches are compatible
Determines the active and standby switch
In VSS WHAT ARE THE TWO MODES A STack can come up?
RPR - Route Processor Redundancy
NF/SSO - Non Stoo Forwarding / Stateful Switchover
In RPR mode how are the planes of the standby switch?
All in standby (control, management, data plane)
In NF/SSO how are the planes of the standby switch?
Management and control plane in standby. Data plane is forwarding
Ce proces de selectie exista in Stackwise pentru a determina Active si Standby switch?
Highest priority ( 1 e default, 15 e cea mai mare)
Lowest MAC Address
Acelasi proces se repeta si pentru electia Standby switch.
Ce lungime au cablurile Stack
0,5m , 1m, 3m
Ce protocol foloseste Stackwise pentru a determina switchurile?
Stack Discovery Protocol (SDP)
Cum se conecteaza switchurile in StackWise Virtual?
Cu SVL - StackWise Virtual Link
Ce trafic trece prin SVL?
Control traffic : se foloseste pentru a stabili domeniul StackWise Virtual
Data traffic: cand traficul primit pe un membru trebuie sa fie trimis pe interfata celuilalt membru
Ce protocoale componente are SVL?
LMP si SDP
Cate moduri de Route Processor Redundancy sunt?
HSA - High System Availability
RPR - Route Processor Redundancy
RPR +
STATEFUL SWITCHOVER (SSO)
Non stop forwarding (NSF)
Graceful Restart (GR
NSR - Non Stop Routing
Ce inseamna SDM si ce face?
Switch Database Management. Te ajuta sa aloci din memoria TCAM pentru diferite scopuri
Destination unreachable este ICMP Type ..?
Type 3
Ce coduri are Icmp destination unreachable?
Cod 0 - destination network unreachable
Cod 1 - destination host unreachable
Cod 2 - destination protocol unreachable
Cod 3 - destination port unreachable
Cod 4 - Fragmentation needed and DF bit set
Cod 13 - Communication administratively prohibited
ICMP type 5 este ?
Redirect
Ce coduri are ICMP Type 5?
Cod 0 - Redirect for network
Cod 1 - Redirect for host
Cod 2 - Redirect for ToS and network
Cod 3 - Redirect for ToS and host
Time exceeded este ICMP Type ..?
Type 11
Ce coduri are ICMP TYPE 11?
Cod 0 - TTL exceeded in transit
Cod 1 - Fragment reassembly time exceeded
Icmp echo request este Type ..?
Dar icmp echo reply?
Echo request este Type 8
Echo reply este Type 0
Cati bytes si ce fielduri are headerul de ICMP?
Are 8 bytes.
Type - 1 byte
Code - 1 byte
Header checksum - 2 bytes
Rest of header - 4 bytes
Ce cod au Icmp echo reply si echo request?
Cod 0
Spune-mi tipurile de ICMPv6
Type 1 - Destination unreachable
Type 2 - Packet too big
Type 3 - Time exceeded
Type 128 - Echo request
Type 129 - Echo reply
Type 133 - Router solicitation
Type 134 - Router advertisment
Type 135 - Neighbour solicitation
Type 136 - Neighbour advertisment
Type 137 - Redirect
Cate tipuri de PA exista in BGP?
Well known mandatory
Well known discretionary
Optional transitive
Optional non-transitive
Ce TTL este setat in iBGP?
255 by default
Ce TTL este setat in eBGP by default?
TTL 1
Tipurile de mesaje din BGP si ce fac
Open - Sets up and establishes the BGP Adjacency
Update - Updates, withdraws , advertises routes
Notification - Indicates an error condition to a BGP neighbor
Keepalive - Ensures that the BGP neighbors are still alive
In BGP OpenSent state ce anume se verifica?
BGP Versions must match
The source IP in the message must match the one configuted for the neighbor
The AS number in the message must match the one configured for the neighbor
BGP RID must be unique
Security parameters must match
Hold time pentru Bgp este!?
180 secunde
In BGP the default keepalive timer is?
60 de secunde. O treime din hold time
BGP Neighbor states
Idle
Connect
Active
OpenSent
OpenConfirm
Established
In BGP Connect neighbor state who manages the connection?
The neighbor with the highest IP address
La ce se refera BGP identifier?
La RID - router ID
Se alege manual
Highest L0
Highest IP Add
Well known mandatory BGP PA Attributes:
Next-Hop – Specifies the next-hop IP address for reaching the advertised prefix. (Modified in eBGP, not in iBGP by default.)
• AS-Path – Lists the AS numbers that a route has traversed. Used for loop prevention (shorter AS-Path is preferred).
• Origin – Indicates how the route was learned:
• i (IGP) – Originated via a network statement in BGP (most preferred).
• e (EGP) – Learned via the obsolete Exterior Gateway Protocol.
• ? (Incomplete) – Learned via redistribution (least preferred).
Well known discretionary BGP PA Attributes
Local Preference – Used within an AS to prefer certain paths (higher is better). Default is 100.
• Atomic Aggregate – Indicates that route summarization has occurred.
Optional Transitive Attributes
Aggregator – Identifies the router (ASN and IP) that performed aggregation.
• Community – Tags routes for policy enforcement (e.g., traffic engineering).
Optional Non Transitive Attributes
Multi-Exit Discriminator (MED) – Suggests which path should be preferred when entering an AS (lower is better).
• Originator ID – Used in Route Reflector (RR) topologies to track the original router advertising the route.
• Cluster List – Also used in RR topologies to prevent routing loops.
BGP best path selection criteria:
Prefer the highest Weight (Cisco-specific)
• The higher the weight, the better. This is a local parameter on Cisco routers.
2. Prefer the highest Local Preference (LOCAL_PREF)
• Higher values are preferred. This attribute is shared within an AS (Autonomous System).
3. Prefer the path originated by the local router (Next-hop = 0.0.0.0 in BGP table)
• If a route originates from the local router (using network or redistribute command), it is preferred.
4. Prefer the shortest AS_PATH
• The path with the fewest AS numbers (hops) is preferred.
5. Prefer the lowest Origin code
• BGP origin codes:
• IGP (i) – Most preferred
• EGP (e) – Less preferred
• Incomplete (?) – Least preferred (redistributed routes)
6. Prefer the lowest MED (Multi-Exit Discriminator)
• Lower values are preferred. MED is exchanged between ASes to influence inbound traffic.
7. Prefer eBGP over iBGP paths
• Routes learned from an external BGP (eBGP) peer are preferred over internal BGP (iBGP) peers.
8. Prefer the path with the lowest IGP metric to the BGP next-hop
• The internal routing protocol (like OSPF or EIGRP) determines the best internal path to reach the next-hop.
9. Prefer the oldest path
• Helps maintain stability by selecting the route that has been in the BGP table the longest.
10. Prefer the path with the lowest neighbor BGP router ID
• If multiple paths are still valid, the one from the router with the lowest BGP router ID is chosen. 11. Prefer the path with the lowest neighbor IP address • If all other attributes are equal, the tie-breaker is the lowest BGP neighbor IP.
DTP HELLO AND HOLD TIMERS
30 seconds and 300 seconds
Cate tipuri de BPDU exista?
Doua. Topology Change Notification
(TCN)
Configuration( Topology Change Acknowledgement - TCA, si TC)
